Add a test for nested structs with same name.

This tests covers an ANGLE bug where nested structs are relabled
incorrectly, giving rise to compile and/or link errors.
Merge pull request #533 from jamiemadill/nested-structs

Add a test for nested structs with same name.
Merge pull request #532 from TiborsHub/master

Improved GLSL constructor expression test message
Conformance test for glsl array of structs with first pos int or bool.

At the time of writing, in Mac OS X with some NVIDIA cards, reading an array of
structs using a loop variable where the struct has an int or bool as its first
member returns corrupted data.

This adds a test with three examples:
- struct with unused int in first position
- struct with unused bool in first position
- struct with used bool in first position
Merge pull request #534 from jenanwise/array-of-struct-with-int-first-position

Conformance test for glsl array of structs with first pos int or bool.
Updated OES_half_float conformance test to ensure uint16 typed data is allowed
Renamed one function for clarity
Merge pull request #518 from toji/uint16_half_float

Updated OES_half_float conformance test to ensure uint16 typed data is allowed