Lasso select tool for masking in sculpting. Initial code, non optimized
for now.
Used to be ultra terrible but with threading (openmp) there is slightly
better performance
and is ready for testing. To use press shift-ctrl-lclick. Still no
ability to
remove mask. Coming soon.

Also make box selection threaded (openmp) and comment fix.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@61002 954f8c5b-7b00-dc11-b283-0030488c597c