include-file paths not expanded

Paths for include-file do not expand the ~ prefix, which would be very helpful because some of us have multiple computers with different usernames. Some of the user-contributed modules use ~ in paths for exec, click-left, etc., so it's strange that it works in some places and not others.

Also variables cannot be used in include paths. Is this a feasible change? I didn't want to open up a separate issue for something so closely-related.