gracefully handle ExitStatus exception in async main loops
 - added readFile and writeFile helpers
 - added default modes to mkdir / mkdev
updated unistd and fs_base tests to use new FS APIs
Simplify some timezone code.

Since we only allow GMT as a timezone and ignore what the browser
says, we can simplify a lot of this code.
Improve CMake toolchain file to use response files. Avoid the compiler detection mechanism that could throw CMake off depending on what is in Windows PATH. Use CMAKE_EXECUTABLE_SUFFIX to specify whether to build .html or .js.
Utilize EM_BUILD_VERBOSE in other.test_cmake.
Delete Emscripten_unix.cmake, the previous commit makes that obsolete!
Add a test to ensure that EMSCRIPTEN=1 variable is set in CMake when building.
Fix other.test_cmake when EM_BUILD_VERBOSE is not defined.
Remove the need to pass CMAKE_MODULE_PATH to CMake by weakly setting it in the toolchain file.
Remove the old mechanism of generating a CMake toolchain file on the fly when 'emconfigure cmake' is called. Instead, the Emscripten toolchain file in Emscripten\cmake\Platform\Emscripten.cmake is always used. This unifies the CMake toolchain handling to use the same toolchain independent of how CMake gets invoked.
Have test_cmake also test that running 'emconfigure cmake' works, in addition to running cmake directly.
Remove default filename suffix specification in CMake toolchain, since test_openjpeg will then fail to configure.
Single quotes for cDefine.
Remove unused / unwritten emlibtool.

This isn't used or even implemented and apparently isn't necessary.
Revert "reimplement getCurrentTime"

This reverts commit bd615f6f4499cc2b928c5603ba98d6bd689e608e.
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.
Adjust EM_BUILD_VERBOSE environment variable to take values 0,1,2 or 3, with the following meanings:

0 - No verbose build. Emscripten will mute stdout and stderr invokations of external tools (configure, cmake, make). Stdout and stderr of those runs will be logged to file (the old mechanism)
1 - Print stderr.
2 - Print stderr and stdout.
3 - Print stderr and stdout, and invoke make with VERBOSE=1.
rearranged FS function order
Merge branch 'vertex_array_object_bug' of github.com:michaeljbishop/emscripten into incoming