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
TACHYON-88 Fix missed Google Java code format.

One of my pet peeve, the indent on switch-case statements:
http://google-styleguide.googlecode.com/svn/trunk/javaguide.html#s4.8.4-switch

In the Switch-case check the contents of a switch block are indented +2.
TACHYON-96 - Change AbstractTachyonFSCore abstract class to TachyonFSCore interface.

I would like to make AbstractTachyonFSCore to be an interface instead:
1. Since AbstractTachyonFSCore does not implement any method, as recommended in effective Java it would be preferable to make it an
interface.
2. For testing purposes, having abstract class does not help to have mock but an interface does.
3. Java class can only extend from one class but can implement multiple interfaces.

This would help pluggability plan that we have for Tachyon APIs.
Remove public accessor for the interface methods.
Interface methods are public by default.
Update Javadoc.
Change fid to fileId to be consistent.