[libfko] add digest verification and length fcns to decode routine
replace malloc() with calloc() calls
[libfko] dedicated parsing functions for decoding client timeout and server auth SPA fields
[test suite] minor bug fix to add udpraw mode for spoofed src test
[libfko] minor error constant label typo fix
[libfko] per-SPA message type field count validation

This commit implements more rigorous SPA packet field count validation
that takes into account expected field counts for each SPA message type.
Two new libfko error codes have been added in support of this, and the
corresponding changes made in the perl and python modules.