Fix EAPI 5 gtk3 not in IUSE

EAPI 5 now dies if we do not have GTK3 in IUSE.

Add the neccesasy DEPEND on gtk+:2/:3 to:
app-text/mate-document-viewer-1.5.0
mate-base/mate-desktop-1.5.6
mate-base/mate-file-manager-1.5.{2,3}
mate-base/mate-session-manager-1.5.1
mate-extra/mate-power-manafer-1.5.1

Add these to profile/package.use.mask
Merge pull request #7 from infirit/EAPI5_ISUE_fixes

Eapi5 isue fixes