The problem was a call to convert_dirname() with a destination buffer
that did not have room for the trailing slash added by that function.
This could cause the instance manager to crash in some cases.


mysys/mf_dirname.c:
  Clarify in comments that convert_dirname destination must be larger than
  source to accomodate a trailing slash.
server-tools/instance-manager/instance_options.cc:
  Fix buffer overrun.