Fix a bug in oes-texture-float.html

If we read from a FBO without alpha, and the read format is RGBA,
alpha should be set to 1.
Merge pull request #546 from zhenyao/fix

Fix a bug in oes-texture-float.html
Added an indexed png with transparent pixels.

I thought there was a bug in the browsers but writing this test
I realize it was wrong. The browsers are already correct.

Whether you think this should be added or not is up to you
Added test for a Chrome regression that corrupted 2D canvas rendering after the canvas was used as a texImage2D source
Added reference to Chrome regression bug
Merge pull request #547 from greggman/add-indexed-png-test

Added an indexed png with transparent pixels.
More consistent use of canvas.width/height instead of hard coded numbers
Merge pull request #548 from toji/canvas_as_texture

Added test for a Chrome regression with canvas 2D
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.