removed dict_contains.py
fixed merge miss in dict.cpp

Rewriter2

Conflicts:
	src/runtime/dict.cpp

ie actually add one.  Before dict.__new__ would simply call
object.__new__ and return something that was very much not a dict :/

Currently returns the address if the Box*

TODO: When using {} to construct the dict, contains works. However
if the dict type is used, the runtime crashes in various ways (see
tests/dict_contains.py)

We were caching certain liveness results (only crawled each BB once
looking for name use/defs), but we were still traversing the entire
CFG for every liveness query.
Now, each query does a single full CFG scan, and computes the results
for all BBs and stores them.

Reduces the time to 'import re' from about 13s to under 2s.

This commit is a straightforward implementation that doesn't include
any speculation-like optimizations.  For operations that can overflow,
just relax the type-return-specification to UNKNOWN, and do the overflow
checks in the runtime.  This means that we no longer emit fast native
integer instructions even if we know operands are ints.

Will have to add optimizations:
- range analysis so that we can know there won't be overflow
- deopt-on-overflow so that we can work with unboxed ints even if there's potential overflow

Augassigns and for loops had an issue where they would try to
do something like 'i = i.__iadd__(j)', ie have multiple operations
in a single statement.  If an exception occurs, it's not clear if
the name got redefined; so far we just assume that it always does (since
we don't have the mechanism to propagate the name along only one
control flow edge).

So we have to split up those multi-operation-statements into multiple
statements.

Fix crash when passing alot of defaults

Implement Python Generators

Conflicts:
	src/codegen/compvars.h
	src/codegen/runtime_hooks.h
	src/runtime/objmodel.h

Just do it by putting a different class object on the same C-level structure.
Not too hard right now to defeat the frozen-ness, please don't try.

Ended up not being too bad, except for some more fun around classdefs
having different rules, and making sure to generate the correct error
type and messages.

Not worth producing CPython's error messages exactly: some delattr
messages depend on whether or not the object has a __dict__ allocated
or not.  Just canonicalize those in the tester.

Merges #101

Conflicts:
	src/codegen/runtime_hooks.h

Conflicts:
	src/codegen/runtime_hooks.h
	src/runtime/builtin_modules/builtins.cpp