Fedora Commons Code

first check in of journaling implementation

integrates journaling change to:
- get dates from the context
- get the would-be-auto-generated-pid from the context,
if in recovery mode (RecoveryContext)
also fixes write concurrency issue by using exclusive,
non-blocking write locks for objects while they're being modified.

implements new reservePIDs and getRepositoryHash methods of DOManager
interface (change for journaling)

added methods to support journaling:
these support journaling but are defined generically
- get repository hash
- never generate pid

marker interface supporting delegate pattern for management
(currently used by journaling)

changes to support journaling:
- dates for API-M operations are always taken from the context
- if in recovery mode (context is RecoveryContext), ids that would
normally be auto-generated are instead taken from the context.

in the event of failure, recovery for writes to lowlevel storage
is more robust.

added method to get date from context, for use while determining
dates for API-M actions

used for recovery from journal

removed license text at top