Fix options with multiple=True on python 3; add tests.
Add a --debug_gc flag to runtests to easily turn on extra logging.
Merge remote-tracking branch 'homm/master'
Use weakrefs instead of __del__ in reference cycle test.

This avoids an awkward and otherwise meaningless use of Task(None).
Prefix all "reserved" names used by the template system with _tt_
to avoid collisions with user-defined names.

Inspired by #768.
Fix locale.format_date on python 3.

There's probably more work to be done on this largely-untested code,
but this was the case I could find by grepping for stray references
to `long`.
Fix a memory leak in HTTPServer with very large file uploads.

This is not quite a true leak since the garbage collector will
reclaim everything when it runs, but it might as well be a leak
because CPython's garbage collector uses heuristics based on the
number of allocated objects to decide when to run.  Since this
scenario resulted in a small number of very large objects, the process
could consume a large amount of memory.

The actual change is to ensure that HTTPConnection always sets a
close_callback on the IOStream instead of waiting for the Application
to set one.  I also nulled out a few more references to break up cycles.

Closes #740.
Closes #747.
Closes #760.
Release note updates.