[TxMt] Open command

[Chuck Esterbrook]

When I hit Command+O, the directory I'm put in is the one for the
project, but I would prefer that the directory match the file that I'm
currently editing (which is often in a subdirectory of the project).

I guess that most of the time I open a file, I'm opening a sibling to
the file I'm currently editing. I have this behavior with UltraEdit on
Windows and find it quite productive.

-Chuck