Prevent disappearing SAD entries by implementing MPsafe refcounting. "Why didn't he use SECASVAR_LOCK()/SECASVAR_UNLOCK() macros to  synchronize access to the secasvar structure's fields?" one may ask. There were two reasons: 1. refcount(9) is faster then mutex(9) synchronization (one atomic    operation instead of two). 2. Those macros are not used now at all, so at some point we may decide    to remove them entirely.
Prevent disappearing SAD entries by implementing MPsafe refcounting.
"Why didn't he use SECASVAR_LOCK()/SECASVAR_UNLOCK() macros to
 synchronize access to the secasvar structure's fields?" one may ask.
There were two reasons:
1. refcount(9) is faster then mutex(9) synchronization (one atomic
   operation instead of two).
2. Those macros are not used now at all, so at some point we may decide
   to remove them entirely.

OK'ed by:	gnn
MFC after:	2 weeks

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