add block handler to handle block files on different under file systems
add BlockHandlerHdfs as stub
change isHadoopUnderFS() in UnderFileSystem to be public, and use it in BlockHandler
modify comment format and gramma mistakes
some format fix
modify according to the comments, format change
fix typo
change error message
clean coode based on comments
add test case for BlockHandlerLocalFS
small format change
some change on code style
change inFilePos from int to long and remote unused IOException
rename BlockHandlerLocalFS and expose FileChannel
modify according to comments
modify interface for append, use ByteBuffer to replace byte[] for zero copy
add checkPermission to BlockHandler's API
Merge pull request #318 from shimingfei/AddBlockHandler

add block handler to handle block files on different under file systems[Tachyon-33][SubTask 1]