Add a sleep function for couchjs test suite tests

CouchJS does not have a sleep function exposed which means it does silly things like request the root url in a tight loop until a timeout is reached.

So it'd be a good idea to add some of these things as C functions to prevent silliness in test suites.

So far this just includes a sleep function that takes a single argument as the number of millseconds to sleep before resuming execution. This is accomplished using Sleep on Windows and usleep on everything else.

These test functions are tied to the presence of a command line switch so that we can ensure that they are not enabled and available to view server scripts by default. The help message has a helpful note to not enable these for production systems.