Fix issue where master HDB can be locked while waiting for network I/O.

Fix issue where master HDB can be locked while waiting for network I/O.

We should not hold locks on the master's database while waiting
for network I/O which may take a terribly long time to complete as
this will block out all writers and could therefore be slightly
problematic.  ipropd-master was holding a shared lock on the database
while sending a complete propation to slaves which are out of sync
with the log file.  We fix this by writing what we intend to send
in record format into a file hdb_db_dir()/ipropd.dumpfile while
holding a shared lock on the database and then we send the contents
of the file after releasing the lock.  We also save and re-use the file
that we generated during future complete propagation events as long
as the log is long enough to get us back to the state previously
dumped.