Merge pull request #1561 from mbebenita/avx

Misc
Add support for log levels (with suppressable output) to IndentingWriter

To be used in the unit testing harness.
Only log passing unit tests in verbose mode

... which is introduced as an `--verbose` option to the grunt setup.

Plus, quit with an error in case of failing unit tests.

Without this, failing unit tests are swallowed in a sea of useless spew, making them very easy to miss.

Also restores the ability to specify which unit tests should be run by using the `--tests=path/to/some/js/files` syntax.
Merge pull request #1562 from tschneidereit/master

Reduce spew from shell unit tests
Only log failing parse attempts for `grunt smoke`
Merge pull request #1563 from tschneidereit/master

Only log failing parse attempts for `grunt smoke`
Show FPS number.
Merge branch 'master' of https://github.com/mozilla/shumway into avx
Clear background when drawing FPS text.