pgsql: Fix syslogger's rotation disable/re-enable logic.

Fix syslogger's rotation disable/re-enable logic.

If it fails to open a new log file, the syslogger assumes there's something
wrong with its parameters (such as log_directory), and stops attempting
automatic time-based or size-based log file rotations. Sending it SIGHUP
is supposed to start that up again. However, the original coding for that
was really bogus, involving clobbering a couple of GUC variables and hoping
that SIGHUP processing would restore them. Get rid of that technique in
favor of maintaining a separate flag showing we've turned rotation off.
Per report from Mark Kirkwood.

Also, the syslogger will automatically attempt to create the log_directory
directory if it doesn't exist, but that was only happening at startup.
For consistency and ease of use, it should do the same whenever the value
of log_directory is changed by SIGHUP.

Back-patch to all supported branches.

Branch
------
REL9_0_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/a6708e2571ac6d2d2b1dc4cdae39acb282c0c5a9

Modified Files
--------------
src/backend/postmaster/syslogger.c | 26 ++++++++++++++++++++------
1 files changed, 20 insertions(+), 6 deletions(-)