Updated cross-origin test in more/functions/texSubImage2DHTML to use newer methodology
Also applying fixes to texImage2DHTML
Merge pull request #560 from toji/cross-origin-2

Updated cross-origin test in more/functions/texSubImage2DHTML
Use a relative rather than an absolute link for the specs/ redirect.

This simplifies local testing of spec changes.
Merge pull request #561 from kenrussell/relative-redirect

Use a relative rather than an absolute link for the specs/ redirect.