PLATFORM= MACOSX10.6 X86_64 MAX

bzr merge 5.5 =>5.6.

Below is a list of issues found during merge.
The changes mentioned below are in addition to
those that come from merge

Problem: sync_io_with_master.inc in 5.5 was renamed to
         sync_slave_io.inc in 5.6 but the source and
         comments in the include file still used 
Fix: Modified source and comments to be in sync with
     the name of the include file.

Problem: The variable $sync_slave_connection was used
         in rpl_sync.inc but it was not cleaned properly.
Fix: Saved the value of $sync_slave_connection, used it
     and then restored the initial value.