Blender Git Loki

A patch set by Bastien Montagne (many thanks!)

* Removed the ../include and ../src include directories from scons/cmake files.
These directories do not exist and are very noisy when building.

* Coding style clean-up in Python scripts: 'string' is used for enum values,
and "string" for usual stings.

* UILayout.active is used instead of UILayout.enabled to grey out "inactive"
settings. This still allows users to edit them, which can be handy sometimes.

* Improved UI layout of the Line Style panel by means of:
- The standard �??column�? paradigm is used in more places;
- More compact layout where possible; and
- Tweaks to the modifiers' header.

* Improved UI layout of the Line Set panel by rearranging the "Selection by"
options into a compact row of toggle buttons.