force usage of internal lua on OS X until someone is willing to properly fix detection cmake code
Revert "force usage of internal lua on OS X until someone is willing to properly fix detection cmake code"

This reverts commit 92f72605dc0439f475f49d2e22d51d3958b09676.
fix build with external lua on OS X
brush masks: small rendering improvement

this fixes a rare rendering issue where brush strokes could have
gaps close to very sharp edges
usermanual: make more clear that bauhaus sliders accept keyboard input