MAJOR: threads/map: Make acls/maps thread safe

MAJOR: threads/map: Make acls/maps thread safe

locks have been added in pat_ref and pattern_expr structures to protect all
accesses to an instance of on of them. Moreover, a global lock has been added to
protect the LRU cache used for pattern matching.

Patterns are now duplicated after a successfull matching, to avoid modification
by other threads when the result is used.

Finally, the function reloading a pattern list has been modified to be
thread-safe.