Blender Git Loki

-> Selection mode switching conversions

Switching between selection modes now converts selections. When
moving to a higher selection mode, selections are flushed 'upwards'
and when moving to lower selection modes selections are flushed 'downwards'.
Unlike old editmesh, selection modes are actually restrictive and elements not
represented by current mode cannot be selected.

Multiselect will take some thought with regards to flushing rules and how tools
should behave.....