MEDIUM: regex: modify regex_comp() to atomically allocate/free the my_regex struct

MEDIUM: regex: modify regex_comp() to atomically allocate/free the my_regex struct

Now we atomically allocate the my_regex struct within function
regex_comp() and compile the regex or free both in case of failure. The
pointer to the allocated my_regex struct is returned directly. The
my_regex* argument to regex_comp() is removed.

Function regex_free() was modified so that it systematically frees the
my_regex entry. The function does nothing when called with a NULL as
argument (like free()). It will avoid existing risk of not properly
freeing the initialized area.

Other structures are also updated in order to be compatible (the ones
related to Lua and action rules).