git-instaweb: Add option to reuse previous config file

Add an option to git-instaweb which allows the usage of the old
gitweb_config.perl situated in '.git/gitweb' dir. When the option
is in use, gitweb_config.perl generated by git-instaweb won't be
overwritten.

Usage:
	git instaweb --reuse-config

Example:
	When I use git-instaweb, it is tiring to add customised
configuration (like highlight featues enabling) to the gitweb_config.perl
file everytime I initiate the server. With this,it's enough to use
this option.

Signed-off-by: Pavan Kumar Sunkara <pavan.sss1991@gmail.com>
Acked-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-instaweb.txt

@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git instaweb' [--local] [--httpd=<httpd>] [--port=<port>]
-               [--browser=<browser>]
+	       [--browser=<browser>] [--reuse-config]
 'git instaweb' [--start] [--stop] [--restart]
 
 DESCRIPTION
@@ -49,6 +49,9 @@ OPTIONS
 	linkgit:git-web--browse[1] for more information about this. If
 	the script fails, the URL will be printed to stdout.
 
+--reuse-config::
+	The previous gitweb_config.perl will not be overwritten.
+
 --start::
 	Start the httpd instance and exit.  This does not generate
 	any of the configuration files for spawning a new instance.

git-instaweb.sh

@@ -13,6 +13,7 @@ p,port=        the port to bind to
 d,httpd=       the command to launch
 b,browser=     the browser to launch
 m,module-path= the module path (only needed for apache2)
+reuse-config    reuse previous gitweb_config.perl from GIT_DIR
  Action
 stop           stop the web server
 start          start the web server
@@ -27,6 +28,7 @@ httpd="$(git config --get instaweb.httpd)"
 root="$(git config --get instaweb.gitwebdir)"
 port=$(git config --get instaweb.port)
 module_path="$(git config --get instaweb.modulepath)"
+no_reuse=true
 
 conf="$GIT_DIR/gitweb/httpd.conf"
 
@@ -151,6 +153,10 @@ do
 		shift
 		module_path="$1"
 		;;
+	--reuse-config)
+		shift
+		no_reuse=false
+		;;
 	--)
 		;;
 	*)
@@ -385,7 +391,7 @@ our \$projects_list = \$projectroot;
 EOF
 }
 
-gitweb_conf
+test "$no_reuse" = true || test ! -e "$GITWEB_CONFIG" && gitweb_conf
 
 resolve_full_httpd
 mkdir -p "$fqgitdir/gitweb/$httpd_only"