Update sysutils/garcon (xfce4 related) and adapt Mk/Uses/xfce.mk for new version

[madpilot]

Summary

This is the first commit in a series I'm going to do related to the XFCE ports. It is required by other bugs with patches I'm going to commit.

The patch unifies Bugs 219928 and 219334 on bugzilla.

I'm requesting approval for the USES file.

[swills]

Works fine for me.

[madpilot]

Testing with non default options showed that disabling the GTK2 option causes failures in other XFCE ports, so I made it a non option.

No change to Mk/Uses/xfce.mk

[mat]

Note that Mk/Uses/xfce.mk is maintained by [e-mail], not portmgr.

[swills]

Fine by me. +1 to what @mat said.