Clean up some miscellaneous warnings from Fortify or Intel's compiler

Clean up some miscellaneous warnings from Fortify or Intel's compiler
Backports;

 r991516, mod_rewrite.c::cmd_rewritecond(): use enum value instead of
          integer literal
 r991515, util.c::ap_pregsub(): don't needlessly set var
 r991507, scoreboard.c::ap_create_scoreboard(): don't needlessly set var
 r987629+r987631, config.c::ap_build_cont_config(): don't needlessly
                  check var for NULL
 r986901+r987860, core.c::dirsection(): remove dead error check
 r983066, mod_cern_meta.c: remove unexpected ";" after end of block
 r987339, main.c::usage(): don't overlay stack buffer with impossibly
          long argv[0]
 r982050, mpm_unix.c (backported to mpm_common.c): remove unused vars

Author: trawick
Reviewed by: sf, wrowe

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1005523 13f79535-47bb-0310-9956-ffa450edef68