help.c: Add support for htmldir relative to git_exec_path()
If htmldir (in the Makefile) is a relative path, this path will now be
interpreted relative to git_exec_path. This can be used to create an
installation that can be moved to a different directory without
re-compiling. The Windows installer (msysgit) is an example for such
a setup.
Note that the Makefile maps htmldir to the define GIT_HTML_PATH.
Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>