Really use /usr/local by default, even on darwin
Really use /usr/local by default, even on darwin

Fixes mypaint/mypaint#60. Missed a line removal in 921de87.

b3sigma/libmypaint,achadwick/libmypaint,achadwick/libmypaint,achadwick/libmypaint,achadwick/libmypaint,b3sigma/libmypaint,b3sigma/libmypaint