Code review comments: use k5_buf, ...

Also provide an accessor for getting the error unadorned.
Don't double-adorn error messages
Don't double-adorn error messages
Don't adorn error messages when logging
Include file ccache name in error messages

Conflicts:
	src/lib/krb5/ccache/cc_file.c
Code review comments about fcc_set_error()
Code review comments for interpret_errno()