Blender Git Loki

Todo item: text editor scroll bar does not respond to clicks

Text space's scroll bar now uses quite the same strategy of handling
drag and click events as view2d.

I tried to share some code between this two spaces. but there was no big
luck with it: text sace uses it's own constants (like scroll bas size and offsets),
so the simpliest way was to define zone stuff for text space without sharing it
with view2d.