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
Fix the bug mentioned in [TACHYON-66]

Fix the bug mentioned in [TACHYON-66] "The memory usage statistics is
not right when multi-user cache the same file and stops their
connection".
add test case for BlockHandlerLocalFS
Change the synchronized range
small format change
[TACHYON-83] Close stream and UnderFS in master image
Fixing EditLog.java
some change on code style
change inFilePos from int to long and remote unused IOException
Fixing code review comments.
rename BlockHandlerLocalFS and expose FileChannel
Add a unit test for cacheBlock

Add a unit test for cacheBlock