The fix to NegateSignatureS caused a test which had been failing
in IsValidSignatureEncoding to then fail in IsLowDERSignature.
Add new test so the original check remains exercised.
NegateSignatureS is called with a signature without a hashtype, so
do not save the last byte and append it after S negation.
Updates the two tests which were affected by this bug.
This fixes a potential race condition in the CCheckQueueControl constructor,
which was looking directly at data in CCheckQueue without acquiring its lock.
Remove the now-unnecessary friendship for CCheckQueueControl
Suhas Daftuar