Fix for Bug #516. Make the GlobalState instance and its constructor not WEAK
Added a test for various uses of Select for the GLSL target.
Merge branch 'master' into glsl-select-tests
GLSL: Fix handling of select

the previous implementation erroneously assumed that the condition of a
select has the same vector width as the arguments, which is obviously
wrong for scalar conditions that don't involve the color dimension.
Add test for GLSL codegen of scalar select conditions
Use extract_lane() instead of custom visitor
Add codegen tests for texture loads
Use explicit init() call instead of static initializer

in the hope that this fixes bug #516
Removed unnecessary include
Merge pull request #518 from halide/glsl-select-tests

Merging