I don't see where RFC1738 disallows periods (.) in URLs. Here are some excerpts from there:
hpath = hsegment *[ "/" hsegment ]
hsegment = *[ uchar | ";" | ":" | "@" | "&" | "=" ]
uchar = unreserved | escape
unreserved = alpha | digit | safe | extra
safe = "$" | "-" | "_" | "." | "+"
So the answer to your question is: Yes, http://www.example.com/module.php/lib/lib.php
is a valid URL.
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