[libfko] fix double free bug in SPA parser

This commit fixes a double free condition discovered through the new
python SPA payload fuzzer.  This bug could be triggered in fwknopd with
a malicious SPA payload but only when GnuPG is used.  When Rijndael is
used for SPA packet encryption, this bug cannot be triggered due to an
length/format check towards the end of _rijndael_decrypt().  It should
be noted that only a person in possession of the correct encryption and
authentication GnuPG keys could trigger this bug.
ChangeLog for 2.6.2
bumped version to 2.6.2
changes since 2.6.1
minor 2.6.2 release date change
changes since 2.6.1
[libfko] bumped version to 2.0.2
changes since 2.6.1
updated RPM Release tag to 1
changes since fwknop-2.6.1