restored type checking
Merge pull request #157 from timeck/restoreTypeChecks

restored type checking in Store.bulkComputeXXX() methods
remove CacheLoader interactions from Ehcache.putIfAbsent() and
Ehcache.replace(K, V)
Merge pull request #153 from timeck/putIfAbsentLoader

remove CacheLoader interactions from Ehcache.putIfAbsent() and Ehcache.replace(K, V)
don't call function twice!
 #35 on-heap by value storage
 #35 rework tests
 #35 fix compiler warning
 #35 improve exceptions
 #35 add serializer exception test
 #35 add by value holder hashcode test
 #35 rename by ref value holder
 #35 refactor OnHeapValueHolder hierarchy
 #35 refactor OnHeapStoreBy(Ref|Value)Test to extract common code