Restore short aliases for DestType enum in nativecalls.cpp

The new names were causing a bunch of merge conflicts and
reduced the signal to noise ratio of the table. This is completely
contained within nativecalls.cpp; the new enum scope is preserved
everywhere else.
Don't use long double

Slots in the x87 stack get marked as occupied when you move
values into the corresponding mmx registers. If you try
to push a value onto the x87 stack, and the slot isnt empty,
it will fail, and give you a nan.

Generally, g++-x64 doesnt use the x87 instructions, but if
you do long double arithmetic, it does. f_pow was using
long doubles - but there was an alternate, much faster, asm
sequence which didnt use long double, and which just needed
to test the right define - so switch to that. Also grep
for long double to make sure we're not using it elsewhere.
Access m_type via helpers.

We had the belief that m_type as an int32_t (and in at least one
place, an int64_t) burned in many places. This is going to make any kind of
re-encoding of TypedValues nearly impossible.

Redirect all such accesses via some helpers, so e.g.

        a.  cmpl(KindOfUninit, base[TVOFF(m_type)]);

becomes

       emitCmpTVType(a, KindOfUninit, base[TVOFF(m_type)]);

which may do byte or dword access, depending on m_type's actual size. While
this is motivated by 7pack, I'm planning to route it through trunk to
prevent any more of the old style accesses from cropping up.
Remove ffi
Disable flaky tests in TestExtFile and TestExtImageSprite
Implement known property offsets in VectorTranslator

This diff implements VectorTranslator::emitPropSpecialized and uses it
in three places: emitProp, emitSetProp, and emitCGetProp. The new test case in
test_code_run.cpp used to crash TranslatorX64; now it throws a fatal to keep
things simple. VectorTranslator has better control flow support at its disposal
and is able to get that case right.
Fix the release build
s/m_contTargets/m_controlTargets/ in emitter.{cpp,h}

contTargets name is misleading and suggests it has something to do with
continuations. Rename it to controlTargets.
ListAssignment: define RHS kind explicitly for all expression types

It's easy to introduce bug by adding a new expression and not defining
its ListAssignment RHS kind. Add all expression types explicitly and
remove default case so that it becomes compile time error if the list is
not updated.