Merging r4013, r4200:

Merging r4013, r4200:

error_log related fixes:

*) Complain on invalid log levels.

   Previously only first log level was required to be correct, while
   error_log directive in fact accepts list of levels (e.g. one may
   specify "error_log ... debug_core debug_http;").  This resulted
   in (avoidable) wierd behaviour on missing semicolon after error_log
   directive, e.g.

       error_log /path/to/log info
       index index.php;

   silently skipped index directive and it's arguments (trying to
   interpret them as log levels without checking to be correct).

*) Fixed configuration summary and manpage contents for the special
   --error-log-path=stderr case.