docs: fix cross-directory linkgit references

Most of our documentation is in a single directory, so using
linkgit:git-config[1] just generates a relative link in the
same directory. However, this is not the case with the API
documentation in technical/*, which need to refer to
git-config from the parent directory.

We can fix this by passing a special prefix attribute when building
in a subdirectory, and respecting that prefix in our linkgit
definitions.

We only have to modify the html linkgit definition.  For
manpages, we can ignore this for two reasons:

  1. we do not generate actual links to the file in
     manpages, but instead just give the name and section of
     the linked manpage

  2. we do not currently build manpages for subdirectories,
     only html

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -270,6 +270,7 @@ technical/api-index.txt: technical/api-index-skel.txt \
 	technical/api-index.sh $(patsubst %,%.txt,$(API_DOCS))
 	$(QUIET_GEN)cd technical && '$(SHELL_PATH_SQ)' ./api-index.sh
 
+technical/%.html: ASCIIDOC_EXTRA += -a git-relative-html-prefix=../
 $(patsubst %,%.html,$(API_DOCS) technical/api-index): %.html : %.txt
 	$(QUIET_ASCIIDOC)$(ASCIIDOC) -b xhtml11 -f asciidoc.conf \
 		$(ASCIIDOC_EXTRA) -agit_version=$(GIT_VERSION) $*.txt
@@ -323,6 +324,7 @@ $(patsubst %,%.html,$(ARTICLES)) : %.html : %.txt
 
 WEBDOC_DEST = /pub/software/scm/git/docs
 
+howto/%.html: ASCIIDOC_EXTRA += -a git-relative-html-prefix=../
 $(patsubst %.txt,%.html,$(wildcard howto/*.txt)): %.html : %.txt
 	$(QUIET_ASCIIDOC)$(RM) $@+ $@ && \
 	sed -e '1,/^$$/d' $< | $(ASCIIDOC) $(ASCIIDOC_EXTRA) -b xhtml11 - >$@+ && \

Documentation/asciidoc.conf

@@ -91,5 +91,5 @@ endif::doctype-manpage[]
 
 ifdef::backend-xhtml11[]
 [linkgit-inlinemacro]
-<a href="{target}.html">{target}{0?({0})}</a>
+<a href="{git-relative-html-prefix}{target}.html">{target}{0?({0})}</a>
 endif::backend-xhtml11[]

Documentation/technical/api-config.txt

@@ -2,7 +2,7 @@ config API
 ==========
 
 The config API gives callers a way to access git configuration files
-(and files which have the same syntax). See linkgit:../git-config[1] for a
+(and files which have the same syntax). See linkgit:git-config[1] for a
 discussion of the config file syntax.
 
 General Usage

Documentation/technical/api-credentials.txt

@@ -180,7 +180,7 @@ longer than a single git process; e.g., credentials may be stored
 in-memory for a few minutes, or indefinitely on disk).
 
 Each helper is specified by a single string in the configuration
-variable `credential.helper` (and others, see linkgit:../git-config[1]).
+variable `credential.helper` (and others, see linkgit:git-config[1]).
 The string is transformed by git into a command to be executed using
 these rules:
 
@@ -293,6 +293,6 @@ helpers will just ignore the new requests).
 See also
 --------
 
-linkgit:../gitcredentials[7]
+linkgit:gitcredentials[7]
 
-linkgit:../git-config[5] (See configuration variables `credential.*`)
+linkgit:git-config[5] (See configuration variables `credential.*`)

Documentation/technical/api-merge.txt

@@ -36,7 +36,7 @@ the operation of a low-level (single file) merge.  Some options:
 	ancestors in a recursive merge.
 	If a helper program is specified by the
 	`[merge "<driver>"] recursive` configuration, it will
-	be used (see linkgit:../gitattributes[5]).
+	be used (see linkgit:gitattributes[5]).
 
 `variant`::
 	Resolve local conflicts automatically in favor