Improve text of README section on Extending Gtk's functionality
Use shorter names for constants, expand exports of constants
Remove _MASK from constant names
fix some GC issues with multiple refs, and changes in Julia base
Add GtkAdjustment, closes #25
Merge pull request #24 from timholy/imageview

Use shorter names for constants, expand exports of constants
Let GtkCanvas objects be double-buffered

This eliminates flicker in ImageView and Winston
Merge branch 'master' of https://github.com/JuliaLang/Gtk.jl into girepo

Conflicts:
	src/gtktypes.jl
	src/gvalues.jl