Fix check-valgrind for the new runtests syntax
Don't check for NULL before calling free

ISO C guarantees free(NULL) will quietly do nothing.
Add a bunch more valgrind suppressions for MIT Kerberos

Some of these may be bugs in MIT Kerberos, but I don't have time
at the moment to investigate.  Most of it appears to be global
data held on to by the library, or new ways in which the PKINIT
OpenSSL plugin leaks memory.