ASN.1: Copy string names to tokens in ASN.1 compiler

Copy string names to tokens in ASN.1 compiler rather than storing a pointer
into the source text.  This means we don't have to use "%*.*s" all over the
place.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: David Woodhouse <David.Woodhouse@intel.com>