fix dynamic runtime op counting

-fix memset bug, sizeof(opcount[MAXO]) == 4, the memset didn't really zero
 anything previously
-Add INIT xsub to zero the counters just before runtime phase entry
-Add END xsub, so getting a snapshot of the runtime counters doesn't
 include any of the ops used to parse the counters/make the table,
 runtime ops now is the exact amount of runtime ops always
-add rcount_all and reser_rcount XSUBs for convience if you want to sample
 the numbers from PP in the middle of your app
-bug fix, move the runtime op counter from running ONCE per runloop entry
 to running for every op
-not loading B::Stats's XS code before runtime phase is wrong, revert parts
 of commit 01231f2642