prepare jpeg as well as jpg
fix gl flush assertion
fix and test glIsProgram
set alpha to false in WebGL rendering - it represents the screen, so no alpha is needed
memory checks for glReadPixels
ensure no writes out of the buffer area in glReadPixels
improve glIsProgram testing
Merge branch 'incoming' of https://github.com/kripken/emscripten.git into incoming
- fixed formatting issues
- bugfix: an existing pointerLockChange handler now gets properly
  removed before it is installed anew
- completed the implementation of the SDL_ShowCursor() function:
  - can now query the current state of the cursor/pointer
  - properly delivers adequate return values
  - added safeguard: when not in fullscreen mode, attempts to
    lock the pointer are ignored as they would fail due to the
    security model of the browser and a return value indicating the
    error is returned

Signed-off-by: Michael Riss <Michael.Riss@gmx.de>
Merge branch 'FullScreenEnhancement' into incoming