/*
* call-seq:
*    rxp =~ string  => int or nil
*
* Matches <code>rxp</code> against <code>string</code>, returning the offset of the 
* start of the match or <code>nil</code> if the match failed. Sets $~ to the corresponding 
* <code>MatchData</code> or <code>nil</code>.
*
*    ORegexp.new( 'SIT' ) =~ "insensitive"                                 #=>    nil
*    ORegexp.new( 'SIT', :options => OPTION_IGNORECASE ) =~ "insensitive"  #=>    5
**/ 
static VALUE oregexp_match_op(VALUE self, VALUE str) {