[krbdev.mit.edu #6618] Support optional creation of PID files for krb5kdc and kadmind

[Greg Hudson via RT]

What I'd like to see, in both cases, is pid file setup moved into a
static helper function.  This would reduce the number of duplicate
cleanup sequences from two to one (both functions would benefit from
flow control which avoids the need for duplicate cleanup sequences, but
that's not your problem) and would also eliminate the need for inner
variable declarations, which are discouraged by our coding practices.

That said, the patches look functionally correct, and it's probably
better to commit them in their current form before the 1.8 branch (which
may happen as early as Monday) than to wait until after for the sake of
cleanliness.