testbench: add test for RainerScript optimizer
bugfix: RainerScript optimizer did not optimize PRI filters

things like "if $syslogfacility-text == "local3"" were not converted
to PRIFILT. This was a regression introduced in 7.5.6.
testbench: improve test
Merge branch 'v7-devel'

Conflicts:
	tests/Makefile.am