CPython does this and seems like a good thing to do.  Otherwise
iterating over a string would cause lots of allocations.

One difference between this implementation and cpython's is that cpython
doesn't eagerly create them, and so it checks to see if they've been
created or not.

Even this is 2x slower

Temporarily disable type speculation

Unfortunately our type speculation strategy has bit-rot
over time, to the point that it's not super helpful.
Deopt (the flip side of the speculation) also has some bugs
in it which I was starting to trigger, so just disable the
whole thing for now.

Turning it off should just be a temporary measure and I'll
look soon into what we need to do to get it back on.

cmake change default build directory, configure script, Fedora support

-pyston build using the copied headers that include the generated pyconfig.h

Conflicts:
	.travis.yml

New benchmarks

Use BoxedString in codegen

Convert to BoxedString much sooner, and have any functions that
might need to box a string take a BoxedString.  This means that
on some paths, we will need to box when previously we didn't, but
for callsites that we control we can just intern the string and
not have to box again.  The much more common case is that we
passed in unboxed string data, but then ran into a branch
that required boxing.

BoxedString shouldn't be that much more costly than std::string,
and this should cut down on string allocations.

For django-template.py, the number of strings allocated drops from
800k to 525k; for virtualenv_test.py, it goes from 1.25M to 1.0M

A couple things made this not 100% mechanical:
- taking advantage of places that we could eliminate unbox/rebox pairs
- different null-termination assumptions between StringRef and the c api.

Based on what Rudi says he was doing (sorry rudi)

Gives you just the top 40 lines.  For use in combination with
watch_%

Add more external projects to our travis-ci test suite

Use the padding bytes at the end of BoxedString

CPython has this optimization as well, and it should
save us an average of 7 bytes per string.

Some `__future__` import stuff

allocate runtime ics using mmap (with PROT_EXEC)

output stderr/stdout diffs for failed tests

free generator even if the don't exit

also, output both in KEEP_GOING mode if VERBOSE

Specify all package versions in virtualenv_test

We were doing this for the main packages, but we would get different
versions of their dependencies dependending on what the latest version
was.

Also, add some extra debugging output in the parser in case that
issue crops up again.

Try to make weakref4 less flaky

Slightly change generator StopIteration handling

Make multiple copies of all of the objects we expect to get
collected, and just assert than any of them get collected.

Unconditionally raise a StopIteration when trying to iterate
a finished generator, regardless of what originally stopped
it from iterating.

Generator: don't generate the traceback for the StopIteration exc when the generator is exiting back to a hasnext call.

Add the _elementtree and update libpypa

Remove redundant code and pave way for #254