Remove the dependency on ant.

The only thing Tachyon uses from ant is LazyFileOutputStream.  Since
this is under the Apache license, it's easier to just include that one
file than to depend on ant.  Depending on ant means that (for example)
Spark jobs get ant jars in their CLASSPATH when using Tachyon, which
they may not want.
Fix buffer usage which results in data corruption in BlockOutStream

Prior to this, use of BlockOutStream.write() with a non-zero offset
would corrupt the block data once we exceed the file limit (default 1MB).
Merge pull request #210 from aarondav/data-corrupt

Fix buffer usage which results in data corruption in BlockOutStream
Merge pull request #209 from cmccabe/remove-ant-dependency

Remove the dependency on ant.