core.whitespace: documentation updates.

This adds description of core.whitespace to the manual page of git-config,
and updates the stale description of whitespace handling in the manual
page of git-apply.

Also demote "strip" to a synonym status for "fix" as the value of --whitespace
option given to git-apply.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -293,6 +293,20 @@ core.pager::
 	The command that git will use to paginate output.  Can be overridden
 	with the `GIT_PAGER` environment variable.
 
+core.whitespace::
+	A comma separated list of common whitespace problems to
+	notice.  `git diff` will use `color.diff.whitespace` to
+	highlight them, and `git apply --whitespace=error` will
+	consider them as errors:
++
+* `trailing-space` treats trailing whitespaces at the end of the line
+  as an error (enabled by default).
+* `space-before-tab` treats a space character that appears immediately
+  before a tab character in the initial indent part of the line as an
+  error (enabled by default).
+* `indent-with-non-tab` treats a line that is indented with 8 or more
+  space characters that can be replaced with tab characters.
+
 alias.*::
 	Command aliases for the gitlink:git[1] command wrapper - e.g.
 	after defining "alias.last = cat-file commit HEAD", the invocation
@@ -378,8 +392,8 @@ color.diff.<slot>::
 	which part of the patch to use the specified color, and is one
 	of `plain` (context text), `meta` (metainformation), `frag`
 	(hunk header), `old` (removed lines), `new` (added lines),
-	`commit` (commit headers), or `whitespace` (highlighting dubious
-	whitespace).  The values of these variables may be specified as
+	`commit` (commit headers), or `whitespace` (highlighting
+	whitespace errors). The values of these variables may be specified as
 	in color.branch.<slot>.
 
 color.pager::

Documentation/git-apply.txt

@@ -13,7 +13,7 @@ SYNOPSIS
 	  [--apply] [--no-add] [--build-fake-ancestor <file>] [-R | --reverse]
 	  [--allow-binary-replacement | --binary] [--reject] [-z]
 	  [-pNUM] [-CNUM] [--inaccurate-eof] [--cached]
-	  [--whitespace=<nowarn|warn|error|error-all|strip>]
+	  [--whitespace=<nowarn|warn|fix|error|error-all>]
 	  [--exclude=PATH] [--verbose] [<patch>...]
 
 DESCRIPTION
@@ -135,25 +135,32 @@ discouraged.
 	be useful when importing patchsets, where you want to exclude certain
 	files or directories.
 
---whitespace=<option>::
-	When applying a patch, detect a new or modified line
-	that ends with trailing whitespaces (this includes a
-	line that solely consists of whitespaces).  By default,
-	the command outputs warning messages and applies the
-	patch.
-	When gitlink:git-apply[1] is used for statistics and not applying a
-	patch, it defaults to `nowarn`.
-	You can use different `<option>` to control this
-	behavior:
+--whitespace=<action>::
+	When applying a patch, detect a new or modified line that has
+	whitespace errors.  What are considered whitespace errors is
+	controlled by `core.whitespace` configuration.  By default,
+	trailing whitespaces (including lines that solely consist of
+	whitespaces) and a space character that is immediately followed
+	by a tab character inside the initial indent of the line are
+	considered whitespace errors.
++
+By default, the command outputs warning messages but applies the patch.
+When gitlink:git-apply[1] is used for statistics and not applying a
+patch, it defaults to `nowarn`.
++
+You can use different `<action>` to control this
+behavior:
 +
 * `nowarn` turns off the trailing whitespace warning.
 * `warn` outputs warnings for a few such errors, but applies the
-  patch (default).
+  patch as-is (default).
+* `fix` outputs warnings for a few such errors, and applies the
+  patch after fixing them (`strip` is a synonym --- the tool
+  used to consider only trailing whitespaces as errors, and the
+  fix involved 'stripping' them, but modern gits do more).
 * `error` outputs warnings for a few such errors, and refuses
   to apply the patch.
 * `error-all` is similar to `error` but shows all errors.
-* `strip` outputs warnings for a few such errors, strips out the
-  trailing whitespaces and applies the patch.
 
 --inaccurate-eof::
 	Under certain circumstances, some versions of diff do not correctly

builtin-apply.c

@@ -45,7 +45,7 @@ static const char *fake_ancestor;
 static int line_termination = '\n';
 static unsigned long p_context = ULONG_MAX;
 static const char apply_usage[] =
-"git-apply [--stat] [--numstat] [--summary] [--check] [--index] [--cached] [--apply] [--no-add] [--index-info] [--allow-binary-replacement] [--reverse] [--reject] [--verbose] [-z] [-pNUM] [-CNUM] [--whitespace=<nowarn|warn|error|error-all|strip>] <patch>...";
+"git-apply [--stat] [--numstat] [--summary] [--check] [--index] [--cached] [--apply] [--no-add] [--index-info] [--allow-binary-replacement] [--reverse] [--reject] [--verbose] [-z] [-pNUM] [-CNUM] [--whitespace=<nowarn|warn|fix|error|error-all>] <patch>...";
 
 static enum ws_error_action {
 	nowarn_ws_error,