Add support for garbage collecting info passed to the plugin before

Add support for garbage collecting info passed to the plugin before
exit to appease address sanitizer's leak detector (and valgrind's
leak checker).  We can't free these sooner since the plugin may be
using the memory.  For plugin API 2.0 it should be make clear that
the plugin must make a copy of the data in the arrays passed in to
the plugin's open() function.  Only enabled if NO_LEAKS is defined.