add_*_vars() speed-up

Based on Rasmus's profiling efforts, we have determined that add_cgi_vars() and add_common_vars() are taking a lot of time. Having taken a look at their implementation it seems that they are doing some unnecessary stuff, like creating a temporary table, filling it with entries and then calling ap_overlap_tables() which is supposed to overlap it over r->subprocess_env. But r->subprocess_env contains only a couple of entries by the time add_common_vars() is called, so it would be faster to add entries to it directly. Also, add_cgi_vars() was doing a subrequest in case r->path_info was present, which is completely unneeded for PHP as Apache module. The solution is to duplicate the functionality of these functions in mod_php5.c which is what the attached patch does. It also sets PATH_TRANSLATED in r->subprocess_env directly, so sapi_apache_register_server_variables() does not need to special case it. Please look it over and test. It seems to give about 7% boost on average. -Andrei