Verify if component values are set correct

GLSL constructors : Added code to verify if component values are set
correct by constructor expression.
Only restore the context on preventDefault

preventDefault() appears to *set* the cancelled flag, so we should abort context restoration if the cancelled flag is *not* set.
Merge pull request #550 from jdashg/context-handle-los

Only restore the context on preventDefault
restoreContext() should INVALID_OP without loseContext()
Add a few more cases for testing struct scope.

Also, move the test from bugs/nested-structs-with-same-name.html
to misc/shader-struct-scope.html.
Merge pull request #551 from jdashg/spec-context-lost-ext

restoreContext() should INVALID_OP without loseContext()
Adjust 00_test_list.txt files.
Merge pull request #552 from zhenyao/scope

Add a few more cases for testing struct scope.
Added test for a shader compiler error when using ANGLE's D3D11 backend
Moved test to glsl/bugs, fixed some minor typos in the test
Merge pull request #554 from toji/d3d11-error

Added test for a shader compiler error when using ANGLE's D3D11 backend
Add test for polygon offset.
Merge pull request #553 from c0d1f1ed/master

Add test for polygon offset.
Removed unnecessary function and enums from EXT_blend_minmax extension spec
Typo. ext -> gl
Merge pull request #555 from toji/ext_blend_minmax_fix

Removed unnecessary function and enums from EXT_blend_minmax spec
Add coverage of uniform structures with non-vec4 elements.

Triggers a uniform packing bug in ANGLE's D3D11 backend.
Merge pull request #558 from vonture/master

Add coverage of uniform structures with non-vec4 elements.
Added link to IP disclosures. Cleaned up name references.
Merge pull request #559 from kenrussell/ip-disclosures

Added link to IP disclosures. Cleaned up name references.