Fixes #26: Package require in project.quill

Unexpected Tcl errors in resulting from erroneous commands in
project.quill led to a stack trace.  The smartinterp used to read
project.quill is now set to remove all standard Tcl commands before
reading the file.

Sometimes it is good to retain standard Tcl commands, as they give more
power to the user; but 'quill add' will eventually be saving
project.quill, which would lose any such usage anyway.