The problem was that the bundled yaSSL library was being built
without thread safety support regardless of the thread safeness
of the compoments linked with it.

The solution is to enable yaSSL thread safety support if any
component (server or client) is to be built with thread support.

Also, generate new certificates for yaSSL's test suite.

config/ac-macros/yassl.m4:
  Enable yaSSL thread safety if linking with the server or a
  thread safe client library. Avoids building a thread safe
  yaSSL when only building a non-thread safe client library.
extra/yassl/CMakeLists.txt:
  Always enable for Windows builds.
extra/yassl/certs/ca-cert.pem:
  New certificate, previous one expired.
extra/yassl/certs/client-cert.der:
  New certificate, previous one expired.
extra/yassl/certs/client-cert.pem:
  New certificate, previous one expired.
extra/yassl/certs/dsa-cert.pem:
  New certificate, previous one expired.
extra/yassl/certs/server-cert.pem:
  New certificate, previous one expired.
extra/yassl/include/lock.hpp:
  Rename MULTI_THREAD to YASSL_THREAD_SAFE.
extra/yassl/src/Makefile.am:
  Use CXXFLAGS to set thread related definitions as the lock header
  (lock.hpp) has no local dependencies.
extra/yassl/src/lock.cpp:
  Rename MULTI_THREAD to YASSL_THREAD_SAFE.
extra/yassl/taocrypt/CMakeLists.txt:
  Always enable for Windows builds.
extra/yassl/taocrypt/benchmark/Makefile.am:
  Pass thread related CXXFLAGS.
extra/yassl/taocrypt/src/Makefile.am:
  Pass thread related CXXFLAGS.
extra/yassl/taocrypt/test/Makefile.am:
  Pass thread related CXXFLAGS.
extra/yassl/taocrypt/test/memory.cpp:
  Rename MULTI_THREAD to YASSL_THREAD_SAFE.
extra/yassl/testsuite/Makefile.am:
  Pass thread related CXXFLAGS.