Allow hippy to read from stdin.
Update hippy docstring, since <file.php> is now optional.
Fix translation.
Never put stdin in the bytecode cache.
Depend upon pexpect.
PYTHONPATH needs to be exported earlier so hippy/main.py sees rpython.
Try once again to set PYTHONPATH in travis tests.
Try explicit passing of pexpect environment.
Try exporting PYTHONPATH explicitly.
Try using an absolute PYTHONPATH.
Merge pull request #66 from hippyvm/read_code_from_stdin

Read program code from stdin when not filename is passed.

Note that pexpect works in a different ${CWD} to usual, so always use an absolute PYTHONPATH.