Builtin git-help.

This patch splits out git-help's functions to builtin-help.c and leaves
only functions used by other builtins in help.c.

First this removes git-help's functions from libgit which are not
interesting for other builtins, second this makes 'git help help' work
again.

Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -519,6 +519,7 @@ BUILTIN_OBJS += builtin-for-each-ref.o
 BUILTIN_OBJS += builtin-fsck.o
 BUILTIN_OBJS += builtin-gc.o
 BUILTIN_OBJS += builtin-grep.o
+BUILTIN_OBJS += builtin-help.o
 BUILTIN_OBJS += builtin-init-db.o
 BUILTIN_OBJS += builtin-log.o
 BUILTIN_OBJS += builtin-ls-files.o
@@ -1085,7 +1086,7 @@ git$X: git.o $(BUILTIN_OBJS) $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ git.o \
 		$(BUILTIN_OBJS) $(ALL_LDFLAGS) $(LIBS)
 
-help.o: help.c common-cmds.h GIT-CFLAGS
+builtin-help.o: builtin-help.c common-cmds.h GIT-CFLAGS
 	$(QUIET_CC)$(CC) -o $*.o -c $(ALL_CFLAGS) \
 		'-DGIT_HTML_PATH="$(htmldir_SQ)"' \
 		'-DGIT_MAN_PATH="$(mandir_SQ)"' \