One of the downsides of the BoxedString-as-attributes change
is that hidden classes become more complicated to gc-scan;
try to claw some of that back.

The real benefit is that we intern the strings that
end up getting used as attribute names, so we can compare
them using pointer comparisons.  It should also reduce
the size overhead of hidden classes, since we no longer
have to copy the string data into the hidden class.

And internStringMortal, which for now just resolves to
internStringImmortal, but lets us mark strings that
could eventually be collected.  (We could use the same
approach that CPython uses and have a string destructor
that removes mortal strings from the intern table.)

Preparation for finalizer code, refactoring some simple_destructor logic.

Convert "a in (b, c)" to "a == b or a == c"

optimize regex handling

some fixes and cleanups

Another 2.7.9 compatibility fix

Do this by adding "contains" to our codegen type system, and
implement a special contains on the unboxedtuple type.

This makes this operation quite a lot faster, but it looks like
largely because we don't implement a couple optimizations that
we should:
- we create a new tuple object every time we hit that line
- our generic contains code goes through compare(), which returns
  a box (since "<" and friends can return non-bools), but contains
  will always return a bool, so we have a bunch of extra boxing/unboxing

We probably should separate out the contains logic from the rest of the
comparisons, since it works quite differently and doesn't
gain anything by being there.

- copy CPython's implementation (that uses C slots)
- implement the C slots for str and list
- avoid doing a division for non-step slices

It was unused

Particularly for string slicing, where we would
always memset the string data to zero, and then
immediately memcpy it.

- put it into a header file (and start including it)
- move the grow-the-array part into a separate function
  to encourage the fast-path to get inlined.

This division is expensive; the divisor is always sizeof(char) or sizeof(Py_UNICODE),
and it seems to be faster to do a branch and then possibly a shift.

int(str) and int(float) don't always return ints (cant return longs, doh).
If we call int() on a subclass of int, we should call its __int__ method in
case the subclass overrode it.

And some other small cleanups

This only does the lexing portion of the process.

Further cut that down into a re.split ubench

Replace the function pointer to the simple_destructor with a boolean
indicating that the tp_dealloc function is safe to call whenever the
simple_destructor used to be instead.

A few additional classes are also specified to have a safe_tp_dealloc.

For exceptions, use a hack where we look for the creation of exception
classes and store them in a list so we can set their destructor at the
same time as other classes.

Some refactors in GC code + class-freed-before-instance bug fix.

Add sre_compile_test.expected

In some rare instances, class objects can be freed before the last
instance of that class, causing a problem in the sweep phase where
we look at the class of the object being freed.

So we keep unreachable classes around for an extra collection to be
safe.

This reverts commit e0bd51eb.

Ie, manually specify the reference output for sre_compile_test.py instead
of running CPython to generate it.  CPython changed the behavior (and interface)
of _optimize_charset at some point between 2.7.7 (where we copied from) and
2.7.9.

We should probably copy their new implementation (seems to have a few more
optimizations), but for now this should fix #707.

jemalloc

some misc microoptimizations

Yes they exist, for example "try getting this attribute
and if it exists call it, otherwise do something else".
Probably not a huge perf improvement since the
exception-throwing will probably dominate.

Use the same "only do this for immortal strings" trick to get
around gc issues.

Only do this for calls with immortally-interned strings so that
we can side-step the track-gc-references-in-ics issue for now.

type speculation support