Added test which shows broken GL emulation when:
1. Binding to a VertexObjectBuffer and calling `glDrawArrays` on two
   different sections of it.
2. Using `glVertexPointer` with actual pointer to a vertex array
   and calling `glDrawArrays` on two different sections of it.
Merge branch 'vertex_array_object_bug' of github.com:michaeljbishop/emscripten into incoming
fix repeated calls to glDraw* where the count changes but not the client attributes; fixes part of #1589
handle glBufferData usages that are not in WebGL; fixes #1589
do not fail in test_dlfcn_qsort of js engine cannot do asm validation; fixes #1591
do not emit externals in side modules
remove no longer needed library.js constants for some libcxxabi stuff, which can confuse INCLUDE_FULL_LIBRARY+exceptions
dlopen+exceptions+asm is not supported yet
longjmp test across asm modules
Merge branch 'incoming' of https://github.com/kripken/emscripten into hp-beta