BigIntegerSerializer, BigDecimalSerializer, TreeMapSerializer and TreeSetSerializer optimizations and enhacements:
  - Proper handle of subclasses (Fix #166)
  - Small optimizations for common BigDecimal and BigInteger constants (Fix #238)
  - Unit test to avoid regression of PermGen leaks (ensure fix of #170 contributed by #173)
Merge pull request #245 from serverperformance/master

BigIntegerSerializer, BigDecimalSerializer, TreeMapSerializer and TreeSetSerializer optimizations and enhacements