Fix typos and grammar in texture size limit tests
Avoid allocating a huge ArrayBuffer in texture-size-limit.html test

Maximum texture size can be quite high even on platforms with limited
memory. Don't allocate a (max size + 1)^2 * 4 byte ArrayBuffer for
testing whether violating the maximum texture size reports an error, but
rather pass null as the texImage2D pixels parameter, so the browser has
the opportunity to check for violations of the texture size limit before
doing large allocations.
Limit memory usage in webgl-compressed-texture-size-limit.html test

This case is more complicated than texture-size-limit, since null can not
be passed to compressedTexImage2D, and so an ArrayBuffer with the correct
size needs to be created to test the size limits. And the texture image
must be square in order to properly test the cube map. Either way, this
patch cuts memory usage of the largest buffer nearly by a factor of four,
which can turn a 1 GB allocation into a more manageable 256 MB allocation
on hardware supporting max texture width of 16384 pixels, for example.

Still, even with this change this test can be a source of failures
related to memory allocation rather than texture size limits.
Change "divisor" to "sizeStep" in compressed texture size limit test
Share an ArrayBuffer among compressed texture size limit test iterations

This will help to reduce CPU memory allocations done by the test. Lack of
GPU memory can still be a problem if the maximum texture size is large.
Merge branch 'master' into texture-size-limit-fix2
Merge pull request #405 from NVIDIA/texture-size-limit-fix2

Fixes to memory allocations in texture size limit testing