The major-version check is now handled by sanitize.  If major
doesn't match, we reject and fall back to the Null object.

Two things:

1. Allow nested Extension lookups.  The offset is always positive, so
it can't loop circularly.

2. Move the check for all Extension subtables having the same lookup
type to the correct place.  Before it wasn't really working.

We can only reuse the ligid if it belongs to a previous ligature, not a
component!

It's not part of the standard and MSVC doesn't like it.  It makes the code
a lot less elegant than it used to be, but I think it should work now.

Bug 591557 – [HB] crash scrolling the evolution message list
Bug 591576 – crashed with SIGSEGV at pango

Apparetly in C++, inline means a totally different thing.