Added a fix of fcrepo-1024 using a new lock-class, StringLock, to ensure that two threads with same PID gets through sequentially.
FCREPO-1024: Added multi-threaded unit tests for DefaultDOManager.getIngestWriter
moving to plain ReentrantLocks and using Mockito/PowerMock
pulling out SQL templates into constants for test support; single-thread unit tests passing
multithreaded test for DefaultDOManager that exercises object locking
clean up http connection handling after redirects in client, some tests