Fix the building of user-manual.texi and gitman.texi documents

Previously "docbook2x-texi" failed to generate user-manual.texi and
gitman.texi files from .xml input files because "iconv" stopped at
"illegal input sequence" error. This was due to some UTF-8 octets in the
input .xml files. This patch adds option --encoding=UTF-8 for
"docbook2x-texi" to allow the building of .texi files complete.
Signed-off-by: NTeemu Likonen <tlikonen@iki.fi>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -187,13 +187,14 @@ git.info: user-manual.texi
 
 user-manual.texi: user-manual.xml
 	$(RM) $@+ $@
-	$(DOCBOOK2X_TEXI) user-manual.xml --to-stdout | $(PERL_PATH) fix-texi.perl >$@+
+	$(DOCBOOK2X_TEXI) user-manual.xml --encoding=UTF-8 --to-stdout | \
+		$(PERL_PATH) fix-texi.perl >$@+
 	mv $@+ $@
 
 gitman.texi: $(MAN_XML) cat-texi.perl
 	$(RM) $@+ $@
-	($(foreach xml,$(MAN_XML),$(DOCBOOK2X_TEXI) --to-stdout $(xml);)) | \
-	$(PERL_PATH) cat-texi.perl $@ >$@+
+	($(foreach xml,$(MAN_XML),$(DOCBOOK2X_TEXI) --encoding=UTF-8 \
+		--to-stdout $(xml);)) | $(PERL_PATH) cat-texi.perl $@ >$@+
 	mv $@+ $@
 
 gitman.info: gitman.texi