[libfko] allow MS compatible usernames

Allow usernames that are compatible with Microsoft guidelines as defined
here:

http://technet.microsoft.com/en-us/library/bb726984.aspx

This allows for greater compatibility between fwknop clients on Windows
(for example that may be deployed with Cygwin) and fwknopd on other
systems.  This change was suggested by Gerry Reno, and tracked by Github
issue #114.
[test suite] allow fuzzing_spa_packet file comments to skip particular packets
[perl FKO module] comment out username fuzzing packets that are now acceptable to libfko
[libfko] start on refactoring fko_decode_spa_data() to put SPA field parsing into dedicated functions
[libfko] call SPA field parsers via function pointers in fko_decode_spa_data()
Merge branch 'master' of https://github.com/mrash/fwknop
Merge branch 'ms_compatible_usernames'

This merges in work on #114 to allow MS compatible usernames, and should
help Cygwin (and Windows) users.
ChangeLog updates for 2.6.1