More intuitive.

Mutex (and Windows.h by extension) are fairly isolated now.

Don't use _cached()

The Win32 definitions for LONG, ULONG, etc conflicts with
hb-open-type.h.  Avoid that by making sure hb-object-private.h
and hb-open-type.h are not included in the same compilation unit.

Needed to be able to include <Windows.h> from hb-object-private.h.

Fixes problem with uninitialized sub_blob->mutex among other things.

Reported by Bradley Grainger.

Patch from Bradley Grainger.

Based on patch by Bradley Grainger.

With this, test/object is now passing.  Yay!

Revealed many bugs in the (untested and known buggy) user_data
support.

Getting the hang of how to cleanly use gtest.

Update to http://unicode.org/iso15924

Fixes some of the test failures in test-unicode with ICU.  Still
one more to fix before the test passes.

Use with --verbose to see what's failing

ICU fails for now.