semantic: Fix wisent parser recursion

semantic: Fix wisent parser recursion

* lisp/cedet/semantic/wisent/wisent.el (wisent-parse): The semantic
 action might be an EXPAND, EXPANDFULL or some similar action calling
 the parser recursively. If the last token of the recursively called
 parsing step failed to match it ends up in wisent-lookahead, and
 function wisent-parse-stream pushs it back onto
 wisent-lex-istream. From there on it simply ends up occuring twice on
 the unmatched-syntax-cache, or worse might even lead to parse errors
 in rare cases.

Copyright-paperwork-exempt: yes