Fix a couple of include tests in repo mode

One just needed to have the file included in the repo.
One was getting the wrong return value (true vs 1).
Free the VarEnv the correct way

detach, rather than destroy.
import curl tests

Not very good coverage here, but @sgolemon predicted that.
Fix runtests to make it workable for contbuild

It wasn't actually decoding test names anymore due to paths
changing; also several slow tests failed when run from the root (which
is where contbuild is going to run them).  Added stuff to make
$HPHP_HOME unnecessary for runtests (contbuild wont have it set), and
fixed a use of $GLOBALS in hphp/test/run to be more php-idiomatic.
Minor tweaks to the IDL

While rewriting gen_ext_hhvm in C++ I discovered these little
anomalies: the "return" field of a function has to exist, and has to be
a dictionary.

I'm also removing the specific class name of hphp_create_continuation as
per the discussion, and removing the support for parsing
types like that.