The following test program will abort in free() if run with MALLOC_CHECK_=2
using glibc-2.2.90-17. I believe this is the cause of the "mcedit crashes on
startup" bug that has been reported several times.

#include <sys/types.h>
#include <regex.h>
#include <stdlib.h>

int
main (int argc, char **argv)
{
  regex_t r;

  regcomp (&r, "^@! */.*/(k|ba||pdk|z)sh", REG_EXTENDED);

  return 0;
}