Since WEBGL_lose_context extension is official now, modify the conformance
tests to test querying this extension. Remove vendor prefix after certain
grace period.
Fixed bug in test expectations of shader-with-illegal-default-precision.vert.html .
Merge pull request #174 from kenrussell/bugfix

Fixed bug in test expectations of shader-with-illegal-default-precision....
Merge pull request #172 from nayankk/context-lose

Test non-vendor prefixed WEBGL_lose_context extension string.