free generator stacks both in the destructor and when a generator exits.

we're already unmapping the redzone as part of the munmap() call.  also, free the generator stack from the sending side, not from within the generator.

a few changes which help out GC performance

when looking up a child hidden class we look up the attr in the child_index map,
then get the HiddenClass* from the children vector (at that index.)

this speeds up GC substantially by letting us visit the range from the vector as
opposed to iterating through the stringmap.

add a map-like container that keeps its values contiguous so we can use the efficient gc_visitor->visitRange.

also, don't register MAX_STACK_SIZE bytes with the GC, register INITIAL_STACK_SIZE.

Somewhat tricky since it assumes __dict__ is always a dict object;
I think I caught most of the places though.

implemented kmod's suggestions

through syntax error when you to `del` a var stored in a closure

add option to tester script to skip specified tests

Conflicts:
	src/codegen/ast_interpreter.cpp
	src/runtime/types.cpp

Update INSTALLING.md

add "sudo" before apt-get
It seems a typo?

add StackRoot<> and #defines for DECREF

add a variadic template ctor that delegates to T's constructor (making things potentially a bit more compact for constructing rooted boxes)

Misc fixes for virtualenv / pip

+ fix a test failing because of a slightly different error message than cpython 2.7.8

Previously we would say that they were coming from the same
file as they are executed in, typically on line 1, which would
give a misleading traceback saying that the module docstring
threw the error.

Now, do what CPython does and say that the file is "<string>",
and don't display the source line.

The method is pretty hacky right now, where it only makes this
adjustment when generating the traceback.  Instead we should probably
get rid of storing the BoxedModule in the sourceinfo in the first place,
and just passing around the relevant info (fn, locals, globals, etc).

Conflicts:
	src/codegen/ast_interpreter.cpp
	src/codegen/irgen/irgenerator.cpp
	src/codegen/pypa-parser.cpp

in merge:
- with_ctxclass_instance_attrs now succeeds due to d1387d74
- merge ~conflict in LangPrimitive opcodes

Remove dbg -O and release -n configurations.

Just for dev; leave Travis-CI the way it is for now.

They test what happens when a weakref's referent gets collected, but
I guess in certain build configurations we would keep the object alive
due to some sort of different memory layout (got saved in a CSR or
a stack slot that didn't get rewritten, etc).

Adding some extra function calls seems to help, though it's hard to tell
how reliable it is.

Misc fixes for pip part 3

Use cpythons isinstance and issubclass implementation

Use the pypa parser as the default parser.

and let the interpreter actually do a cls lookup when encountering a ClsAttribute node...

but both args have to fit into an int...

This commit removes our implementation of this functions,
because they could not handle mixing of old and new style classes.
And having two implementations with very similar name but different
results is very confusing.
Also adds __subclasscheck__ and __instancecheck__ support