Use pkg-config to check for zlib
Remove zlib status from summary

Because zlib is considered as required since commit 6c5b6a2ec,
we don't need to show if zlib support is enabled or not in the
settings summary.
Adding options for tcp keep alive.
regression fix: build problems in debug build
fix interface versioning after recent extension
Fixing bug in plugin.pl that would cause it to never terminate when rsyslog ends a EOF.
Fixing spaces vs tabs
fix spelling of comment
Merge branch 'make-zlib-required' of https://github.com/Whissi/rsyslog into master-candidate
configure.ac: fix the mix-up between enable_rsyslogd and enable_extended_tests
testebench: mitigate UDP message loss

in legacy config, we do not have a way to slow down sending
UDP messages to a rate where no message loss occurs (message
loss is fine here due to the UDP RFCs!). As such, we simply
reduce the number of messages in this test. That actually
doesn't hurt anything, as the purpose of the test is that
messages are properly received and processed.

More messages are still being sent with the equivalent test
that uses RainerScript config.