multiple Token classes in Parser may have same regexp

It is now possible for multiple token types in a Parsers items list to have
the same rx attribute. In this case the token type test_match() method is
called for all but the last one in the list. The first one returning true is
used.
use the new possibility in slexer for multiple token types to have the same rx and use test_match() to distinghuish token type based on word lists, avoiding too long regexps.
add inf and nan to scheme number