web--browse: Add support for xdg-open

xdg-open is a tool similar to git-web--browse.  It opens a file or URL in the
user's preferred application.  It could probably be made default at least on
Linux with a graphical environment.

Signed-off-by: Rüdiger Sonderfeld <ruediger@c-plusplus.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-web--browse.txt

@@ -35,6 +35,7 @@ The following browsers (or commands) are currently supported:
 * open (this is the default under Mac OS X GUI)
 * start (this is the default under MinGW)
 * cygstart (this is the default under Cygwin)
+* xdg-open
 
 Custom commands may also be specified.
 

git-web--browse.sh

@@ -34,7 +34,7 @@ valid_tool() {
 	firefox | iceweasel | seamonkey | iceape | \
 	chrome | google-chrome | chromium | chromium-browser | \
 	konqueror | opera | w3m | elinks | links | lynx | dillo | open | \
-	start | cygstart)
+	start | cygstart | xdg-open)
 		;; # happy
 	*)
 		valid_custom_tool "$1" || return 1
@@ -112,7 +112,7 @@ fi
 
 if test -z "$browser" ; then
 	if test -n "$DISPLAY"; then
-		browser_candidates="firefox iceweasel google-chrome chrome chromium chromium-browser konqueror opera seamonkey iceape w3m elinks links lynx dillo"
+		browser_candidates="firefox iceweasel google-chrome chrome chromium chromium-browser konqueror opera seamonkey iceape w3m elinks links lynx dillo xdg-open"
 		if test "$KDE_FULL_SESSION" = "true"; then
 			browser_candidates="konqueror $browser_candidates"
 		fi
@@ -179,7 +179,7 @@ konqueror)
 		;;
 	esac
 	;;
-w3m|elinks|links|lynx|open|cygstart)
+w3m|elinks|links|lynx|open|cygstart|xdg-open)
 	"$browser_path" "$@"
 	;;
 start)