Fix deadlock issue in freeBlock
Merge pull request #165 from colorant/lock

Fix deadlock issue in freeBlock
Merge pull request #167 from Du-Li/master

under FS prefix file:// should be treated the same as local FS
This commit fixes loadufs command line to take parameters: bin/tachyon loadufs <TachyonPath> <UnderfsPath> [<Optional Excluding Prefixes;>]

(1) It adds a new method UnderfsUtil.getInfo/5 for implementing the new loadufs command line while keeping the old getInfo/4 for compatibility.
(2) It adds toString methods in PrefixList and TachyonFS for printing meaningful debug messages.
(3) It fixes list() in UnderFileSystemSingleLocal to return absolute paths, to be consistent with UnderFileSystemHdfs.
(4) It smooths out the uses of list() in other modules.
(5) It fixes docs/Syncing-the-Underlying-Filesystem.md accordingly.