Include proc line number in error stack trace.

[wduquette]

Standard TCL stack traces include the number of the line in a procedure where the error occurred.

[ ] Track the script line number when parsing.
[ ] Save the line number in WordVec
[ ] Retrieve and include in the stack trace in Interp::eval_script.
[ ] Set the line number in the ErrorData
[ ] Support -errorline in return and catch