Patch for reserved connections for replication users

Hi,

this patch introduces a new configuration flag
replication_reserved_connections to reserve connection slots for
replication in the same way superuser_reserved_connections works for
superusers.

This helps in cases where the application opens connections until
max_connections is reached. A slave would not be able to connect to the
master now and would just be down. With this patch the slave is able to
connect.

This option does not influence the superuser_reserved_connections, so
new slaves are not able to open new connections when the reserved
replication slots are filled.

The only thing this patch is missing are tests. Where should I put them
into the source tree?

thank you,

Stefan Radomski