* Add pooled_secure_allocator and mt_pooled_secure_allocator
* Use mt_pooled_secure_allocator for BLS secure allocation
The old solution relied on thread-local-storage and was thus not compatible
to libc6 2.11 (which is the minimum supported version we use).
Also, the old solution turned out to be erroneous. It would have crashed
or memory leaked when ownership of CBLSPrivateKey would be handled over
to another thread.
* Add new header files to Makefile.am
* Fix copyright headers of new files
* Bail out early from secure deallocation
* Clean up global BLS keys when shutting down
* Move handling of size >= SerSize into SetBuf/GetBuf
Instead of performing this in the individual implementations of
InternalSetBuf and InternalGetBuf
* Assert that size if GetBuf is always SerSize
