Gove LockInfo a Marshal method for easy serialization, and a String
method for more readable output.
Have the state.Locker implementations use LockError when possible to
return LockInfo and an error.
The new test pattern is to chdir into a temp location for the test, but
the prevents us from locating the testdata directory in the source. Add
a source path to testLockState so we can find the statelocker.go source.
James Bardin