embryonic facility for pseudo-modal dialogs.
* stdwinevents.py: added modifier masks for key/mouse events
* renamed exceptions in nntplib.py
* Changed string.join() to call string.joinfields() to profit of
strop.joinfields()
* changed eval() into getattr() in cmd.py
* added dirname(), basename() and (dummy) normath() to macpath.py
* renamed nntp.py to nntplib.py
* Made string.index() compatible with strop.index()
* Make string.atoi('') raise string.atoi_error rather than ValueError
* Added dirname() and normpath() to posixpath.