syslog configurable line splitting behavior

Writing log messages to syslog caters to ancient syslog implementations
in two ways:

- sequence numbers
- line splitting

While these are arguably reasonable defaults, I would like a way to turn
them off, because they get in the way of doing more interesting things
with syslog (e.g., logging somewhere that is not just a text file).

So I propose the two attached patches that introduce new configuration
Boolean parameters syslog_sequence_numbers and syslog_split_lines that
can toggle these behaviors.