Revision 1166417

FLUME-760. First patch.

This patch tweaks the Channel and Transaction interface to establish
the transaction use idiom. The implementation of NullSink, LoggerSink,
RollingFileSink as well as that of MemoryChannel has been updated 
according to these changes.

Also introduced in this commit is a new module for JDBC channel 
implementation which is currently a stub that will get populated with
future commits.