Add line numbers to all exception messages.

This stores the filename, line number, and column number directly in the exception object.  This does two things:

1) It provides significantly more flexibility in creating error messages.  By modifying tp$str and/or the skulpt wrapper, the exception messages can be more easily tailored to the system.

2) It allows all exception messages to include "on line XXX" without having to go in and modify every exception where it is thrown.  tp$str now does this by default.

This is the improvement of commit 2316e1474faa2cbc90546995048ca15020fd1280, which was rolled back in anticipation of this change.