Documentation/Makefile: Some `git-*.txt' files aren't manpages.

In particular, git-tools.txt isn't a manpage, and my Asciidoc gets upset
by it.  The simplest fix is to Remove articles from the list of manpages
the Makefile.

Signed-off-by: Mark Wooding <mdw@distorted.org.uk>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/Makefile

@@ -1,4 +1,7 @@
-MAN1_TXT=$(wildcard git-*.txt) gitk.txt
+MAN1_TXT= \
+	$(filter-out $(addsuffix .txt, $(ARTICLES) $(SP_ARTICLES)), \
+		$(wildcard git-*.txt)) \
+	gitk.txt
 MAN7_TXT=git.txt
 
 DOC_HTML=$(patsubst %.txt,%.html,$(MAN1_TXT) $(MAN7_TXT))
@@ -11,6 +14,7 @@ ARTICLES += howto-index
 ARTICLES += repository-layout
 ARTICLES += hooks
 ARTICLES += everyday
+ARTICLES += git-tools
 # with their own formatting rules.
 SP_ARTICLES = glossary howto/revert-branch-rebase