[krbdev.mit.edu #6124] ccache auxilliary functions

[Justin Anderson via RT]

To allow for the creation of KIM, the following additions need to go into the krb5 ccache and 
cccol code:

- krb5_cc_lock/unlock to explicitly lock editing of a ccache
- krb5_cccol_lock/unlock to explicitly lock creation and deletion of all ccache
- krb5_cc_last_change_time to monitor changes to ccaches
- krb5_cc_move to migrate a ccache across cache types
- add missing pertype cccursor support to ccache types to allow iteration of all available ccaches