Added isDirectory to tachyon file, added directory check in mkdir tests
update JIRA url.
Update README.md
Merge pull request #26 from markhamstra/DebPackaging

Deb packaging
Make UserInfo more efficient, plus more tests.
Merge branch 'master' of github.com:amplab/tachyon
remove jdk requirement in deb packaing.
dep on hadoop-client only.
separate worker's rpc handler and storage server.
Separate worker info usage for master and workers.
Improve worker storage related.
fix tests.
active remove.
Tachyon FS and Hadoop FS nameing.
add timeout logic for master client.
better stop logic for HeartbeatThread, and better naming for master client.
add worker client heartbeat, remove the heartbeat in tfs client.
1. add getSpace for underfs. 2. rename static getXXX() to be get()
remove clientfileinfo from tachyonfile.
Merge branch 'master' of https://github.com/amplab/tachyon