[color] allow alpha to omitted when converting from strings
[color] allow alpha to omitted when converting from strings

Parse #rgb and #rrggbb in addition to forms with the alpha channel
specified. This allows conversion of colour strings from documents such as
CSS where the alpha channel is not specified when using '#' notation.

ebassi/clutter,jigpu/clutter,djdeath/clutter,djdeath/clutter-multithreaded,djdeath/clutter-multithreaded,jigpu/clutter,kerrickstaley/clutter-vala,djdeath/clutter-android,nobled/clutter,dlespiau/clutter,djdeath/clutter,Distrotech/clutter,Distrotech/clutter,collects/clutter,spatulasnout/clutter,Distrotech/clutter,GNOME/clutter,dlespiau/clutter,ebassi/clutter,GNOME/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,ebassi/clutter,nobled/clutter,jigpu/clutter,Distrotech/clutter,heysion/clutter-clone,rkudiyarov/clutter_osx,Distrotech/clutter,GNOME/clutter,jigpu/clutter,jigpu/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,spatulasnout/clutter,djdeath/clutter-android,jigpu/clutter,rkudiyarov/clutter_osx,GNOME/clutter,collects/clutter,ebassi/clutter,djdeath/clutter-android,spatulasnout/clutter,djdeath/clutter-android,spatulasnout/clutter,djdeath/clutter,collects/clutter,nobled/clutter,GNOME/clutter,djdeath/clutter-multithreaded,djdeath/clutter,rkudiyarov/clutter_osx,collects/clutter,ebassi/clutter,rkudiyarov/clutter_osx,djdeath/clutter,Distrotech/clutter,dlespiau/clutter,heysion/clutter-clone,spatulasnout/clutter,heysion/clutter-clone,djdeath/clutter,djdeath/clutter-android,collects/clutter,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded