Same logic as Indic and SEA.

These were never tested with Indic shaper, and indeed wouldn't work there
because they didn't have their viramas and other config defined.  They are
all also supported by MS through USE, so route them there.

This makes USE feature-complete as far as the Indic-like features
are concerned.

Unused right now.

And add check to FLAG()

Still no reordering.

Don't reroute scripts that we were routing to other shapers
before (just yet).

Even compiles.

Positional sub-categories not applied yet.

The spec wrongly has "H" where "HN" is meant.

Grammar from the spec!

Based on https://bugzilla.mozilla.org/show_bug.cgi?id=1183209

https://bugs.freedesktop.org/show_bug.cgi?id=91228

Commit cdcdfe61 changed two `#pragma
message` to `#pragma error` in hb-unicode.cc, however MSVC uses #error,
just like the #else branch. `#pragma error` is an unknown pragma so
MSVC does not fail the build because of it, which I believe was the
intention of that commit.

If it's meant to be an #error, then the #ifdef for _MSC_VER can be
removed entirely.

Fixes test-shape, and:
https://code.google.com/p/chromium/issues/detail?id=497578

Separate the loops for the two cases of replacing with space
and deleting.  For deleting, use the out-buffer machinery.

Needed for upcoming cluster merge fix.

Based on test from https://code.google.com/p/chromium/issues/detail?id=497578

Currently fails.  Basically, if there's a default_ignorable at the
start of text, and font has no space glyph, we remove the default_ignorable,
and that makes the first char in text to correspond to no cluster.

Fix coming.

Until I figure out what to do about the API, and finalize
the tool.

Part of https://github.com/behdad/harfbuzz/issues/91

First try...