Fix regex abort when it tries to reenter itself

Fix regex abort when it tries to reenter itself

Problem reported by Ken Raeburn.
Solution suggested by Stefan Monnier (Bug#21688).
* src/regex.c (re_match_2_internal):
Use new _FAST functions to avoid regex code reentering itself.
* src/syntax.c (update_syntax_table_forward): New arg PROPERTIZE.
All callers changed.
* src/syntax.h (UPDATE_SYNTAX_TABLE_FORWARD_FAST)
(UPDATE_SYNTAX_TABLE_FAST): New inline functions.