Small fixes for the baseline JIT

Fix irgen bug for instancemethods

We would try to statically-resolve their getattrs, but there's some
special casing in the getattr logic for them.  Which should be handled
by moving the special-case to a proper tp_getattr, but for now just
add the special-casing to "hasGenericGetattr" as well.

Refactor offset macros to use the C++ built-in instead.

More small improvements

This probably doesn't matter that much since I don't
think the function names get used during execution,
but they get seen by tools/annotate.py

ie instead of generating the call to compare(AST_TYPE::Is), just
directly do the pointer comparison in LLVM IR.

For c extension classes that define it.  This makes
unicode-subscripting much faster.

An assortment of misc small perf changes

Put the common-case (where we don't do any work) in an
inline-able function, and keep the slow stuff hidden.

At this point, this is only used for some rarely-used
targets like "disassemble this bitcode".

Plus a benchmark of the getattr() function.
I have some ideas on how to make this faster, but I don't
think it's that important at the moment.

Be more consistent about "ip" while unwinding

rewriter optimization; switch things away from compareInternal

rewriter: use lea to allocate stack space

compareInternal should probably just call PyObject_RichCompareBool
eventually, but the switch also has the benefit of avoiding an
extra boxing step.

Unicode-creation optimizations

I think the ip we receive is the return address to that stack frame
(at least in the non-signal case).  This makes things a bit weird
since the "is this ip in this range" tests have a different half-openness
than they normally do.  At some point an "ip = ip - 1" snuck in, which
I think was to address this issue, but I think it's better to not
change the ip -- ie the resulting address is not independently useful (it's
in the middle of an instruction); we could pass it around as "ip_minus_one",
but instead just try converting the tests to be better.

Since we don't memset the unicode allocations any more, and
we now use a precise gc handler, we have to be careful that
unicode objects are valid enough whenever a collection could
happen.

The issue was that "unicode->str = gc_alloc(...)" could cause
a collection, in which case the collector would go and see a
bogus value in the ->str field.  Now, do the str allocation
first (since it is UNTRACKED) and then do the precise allocation
second.

Inlining the allocation + object initialization saves
a decent amount of overhead, since most of the properties
will be fixed.  For example, the size of the main allocation is
fixed, so we can directly allocate it from the correct SmallArena
bucket.  We can also skip all the indirect function calls.

add babel to our extra tests

baseline jit: patch block transitions to a direct jump.

Add a new JIT tier which is tightly coupled to the AST Interpreter

+ add small cleanup: add helper for mode calculation

For issue #254, add lt, le, gt, ge to old-style class