Blender Git Loki

Text space fixes:

- Bring back cursor set to PRESS event - block selection wouldn't
have correct start position;
- Undo stack push was missed in cursor_set operator;
- Remove unneeded cursor moving at set_selection operator;
- Fixed bug with scroll bar - it shouldn't use EVT_TWEAK;

There could be still small issues with selecting single character by
mouse (due to EVT_TWEAK threashold), but this operator is for block
selection, not single char. So shouldn't be big pain here.