Functional tests do not pass on Windows

[chwarr]

The functional tests do not pass on Windows. I've found three issue so far. (Let me know if you want me to open these as different issues.)

• [x] The call to stop-process fails on Windows with the error "No SIGTSTP support". Potential fix is to skip stop-process if Windows is detected was merged with #43..
• [ ] (sleep-for n) doesn't pause reliably for me (I'm using GNU Emacs 24.5.1). This may be due to a known bug.
• [ ] The secure websocket test fails to connect with the message "gnutls.c: 1 GnuTLS library not found". Probably want to test whether there's TLS support and only run the test if there is.

[ahyatt]

About the last issue - there is a function, `gnutls-available-p', but on my machine it returns nil even though I have gnutls and can form wss connections. This could be because gnutls wasn't actually used, but another library like openssl was. I don't think there is a comprehensive way to check for this beforehand, but I can add a note in the test for windows users.

An even better solution would be fail with a useful error message when gnutls is not found. A pull request that does that would be welcome!

[ahyatt]

Checked in bcbd5258b2fd14e12e9a8c9d89cc2d727b5a8da0 with the note.