Don't try to stat() not-on-disk ccache residuals

Don't assume that source ccache residual names are filenames which we
can stat() usefully, but try to keep doing so when they at least name
items with pathnames (i.e., files and directories).
Pass a missing argument to fprintf()
Mark krb5_store_some/all_creds as static

Both krb5_store_some_creds and krb5_store_all_creds are only defined and
called from one source file, so mark them as static functions.
Remove "other" creds arrays, which are always NULL
Make show_credential static, too
Remove unused compare_creds() function
Remove a redundant copy of an argument pointer
Remove no-longer-used krb5_ccache_overwrite()
Removed no-longer-used krb5_find_princ_in_cache()
Fix minor memory leak
Copy config entries to the target ccache

When we try to screen out expired creds while reading them from one
ccache to eventually store in another, also keep configuration entries.