Fix typo in t_credstore.c

Correctly check whether the next argument is NULL in the while loop
which parses store elements.
Clean up python bytecode from doc build

Otherwise they escape into the release tarball.
Add a krb5-config man page

Missed when converting the old nroff man pages.
Regen man pages to pick up krb5-config

Also some other small changes and the copyright date range.