check-for-changes.sh did not have a special case to handle lines in
postfix-relaymap.cf consisting of only a domain (indicating that said
domain should never be relayed). This case is handled by
start-mailserver.sh so when such a line existed, things would work well
until a config file update was detected by check-for-changes.sh. After
that, the generated relayhost_map file would be corrupted.
Fixed by factoring a 'populate_relayhost_map' function out of
start-mailserver.sh and into helper_functions.sh and reusing it in
check-for-changes.sh.
Note: There are certainly quite a few more pieces of code that could be
refactored in a similar fashion.
Note2: check-for-changes.sh would previously never update the
relayhost_map file when $ENABLE_LDAP was set to 1. I don't think this
was intended —there is after all no such condition in
start-mailserver.sh— and so this condition no longer applies.
