Issue 179: XAttr first stable version for main logic review. (weilin)

[weilintsaiWand]

Link to #179

[weilintsaiWand]

Summary of changes for init commit:

• Add new CF "xAttrColumnFamily"
• XAttr related methods done with 40 unit tests
• The prefix (such as "user.") will inserted to HBase, too. For instance, there's a column named "user.attr1"
• Add some methods in INodeManager. Do not change/use any existed methods in INodeManager. That is say, getINode and updateINode does not load/set any XAttr related data.
• Add permission checking.
• Add configuration checking and its tests (maybe in TestGiraffaFSNegative)

[shvachko]

Let's try to keep reviews in the issue rather than in the pull request next time.