Documentation: stop depending on Perl to massage user manual

The "fix-texi.perl" script is used to fix up the output of
`docbook2x-texi`:

  - It changes the filename to be "git.info".

  - It changes the directory category and entry.

The script is written in Perl, but it can be rather trivially converted
to a shell script. Do so to remove the dependency on Perl for building
the user manual.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

Documentation/Makefile

@@ -398,9 +398,9 @@ user-manual.html: user-manual.xml $(XSLT)
 git.info: user-manual.texi
 	$(QUIET_MAKEINFO)$(MAKEINFO) --no-split -o $@ user-manual.texi
 
-user-manual.texi: user-manual.xml
+user-manual.texi: user-manual.xml fix-texi.sh
 	$(QUIET_DB2TEXI)$(DOCBOOK2X_TEXI) user-manual.xml --encoding=UTF-8 --to-stdout >$@+ && \
-	$(PERL_PATH) fix-texi.perl <$@+ >$@ && \
+	$(SHELL_PATH) fix-texi.sh <$@+ >$@ && \
 	$(RM) $@+
 
 user-manual.pdf: user-manual.xml

Documentation/fix-texi.perl

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+awk '
+	/^@setfilename/{
+		print "@setfilename git.info"
+		next
+	}
+	/^@direntry/{
+		direntry=1
+		print "@dircategory Development"
+		print "@direntry"
+		print "* Git: (git).           A fast distributed revision control system"
+		print "@end direntry"
+		next
+	}
+	/^@end direntry/{
+		direntry=0
+		next
+	}
+	!direntry
+'