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!