grep.c: add configuration variables to show matched option

To support git-grep(1)'s new option, '--column', document and teach
grep.c how to interpret relevant configuration options, similar to those
associated with '--line-number'.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1183,6 +1183,8 @@ color.grep.<slot>::
 	function name lines (when using `-p`)
 `lineNumber`;;
 	line number prefix (when using `-n`)
+`column`;;
+	column number prefix (when using `--column`)
 `match`;;
 	matching text (same as setting `matchContext` and `matchSelected`)
 `matchContext`;;
@@ -1797,6 +1799,9 @@ gitweb.snapshot::
 grep.lineNumber::
 	If set to true, enable `-n` option by default.
 
+grep.column::
+	If set to true, enable the `--column` option by default.
+
 grep.patternType::
 	Set the default matching behavior. Using a value of 'basic', 'extended',
 	'fixed', or 'perl' will enable the `--basic-regexp`, `--extended-regexp`,

Documentation/git-grep.txt

@@ -44,6 +44,9 @@ CONFIGURATION
 grep.lineNumber::
 	If set to true, enable `-n` option by default.
 
+grep.column::
+	If set to true, enable the `--column` option by default.
+
 grep.patternType::
 	Set the default matching behavior. Using a value of 'basic', 'extended',
 	'fixed', or 'perl' will enable the `--basic-regexp`, `--extended-regexp`,

grep.c

@@ -96,6 +96,10 @@ int grep_config(const char *var, const char *value, void *cb)
 		opt->linenum = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp(var, "grep.column")) {
+		opt->columnnum = git_config_bool(var, value);
+		return 0;
+	}
 
 	if (!strcmp(var, "grep.fullname")) {
 		opt->relative = !git_config_bool(var, value);
@@ -112,6 +116,8 @@ int grep_config(const char *var, const char *value, void *cb)
 		color = opt->color_function;
 	else if (!strcmp(var, "color.grep.linenumber"))
 		color = opt->color_lineno;
+	else if (!strcmp(var, "color.grep.column"))
+		color = opt->color_columnno;
 	else if (!strcmp(var, "color.grep.matchcontext"))
 		color = opt->color_match_context;
 	else if (!strcmp(var, "color.grep.matchselected"))