Performance improvement for test-device.

When we detect that a page is color, set the ignore image hint
to avoid us loading future images. The overhead on loading
images is not generally huge, except for JPEG2000 ones, which
currently require decoding at load time. This therefore saves
lots of time for such files.

Also, a tiny tweak to ignore page components with 0 alpha.
Clean some whitespace.
Add locale-independent number formatting and parsing functions.
Add fz_snprintf and use it for formatting floating point numbers.
Update MuJS thirdparty module.
Fix memory leaks in test_device.

We were failing to drop each pixmap after testing it, and to free
the test_device structure at the end of each run.
Fix windows build breakages due to missing NAN and INFINITY.

Add some #definery for platforms where NAN and INFINITY aren't
defined in std headers.