Invoke do script with filename and not full path

Since the do script is run in its directory, it can be safely, and more correctly,
invoked with its basename and not a fullpath.
replace doPath variable with more correct doDir
Run .do script in own directory and make paths relative.

Do scripts now run in their own directory
Arguments $1 and $2 include relative paths from the do script directory.
Do script search for targets with multiple extensions uses extension suffixes,
not prefixes.