Fix bugs in inform_dist_infer and accumulate
Fix bugs in inform_dist_infer and accumulate

1. Fix a signed/unsigned comparision warning
   This was a problem on its own, but it became a bug when we
   fixed it.
   Specifically, this was causing negative events to be caught
   because they were begin implicitly cast to unsigned
   values and, thus, compared as greater than the size of the
   distribution's support. When we cast the sizes to signed
   integers, negative events were not being caught.

2. Fix a double free error in inform_dist_infer
   The base needs to be reset if an invalid event is found so that
   a distibution is never constructed and accumulate is never called.

ELIFE-ASU/Inform,ELIFE-ASU/Inform,dglmoore/Inform,dglmoore/Inform