Add compatibility function for older libkrb5
Before krb5 1.13 the krb5_salttype_to_string() function was returning
incorrect names (display names of some kind instead of the names
used by the rest of the library to map saltname to the salt type
integer number).
This patch adds a function that checks at runtime if we have a working
function and uses a fallback map updated to the salt types known up
to 1.12, this allows us to use the library provided function in
following releases where new salt types may emerge.
Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Milan Kubik <mkubik@redhat.com>