Use the "recent time" cache to optimize timestamp generation for

Use the "recent time" cache to optimize timestamp generation for
the httpd error log

Background: According to some profile data that we collected on Solaris,
half the run time of ap_log_rerror() was spent in localtime(3).   With
this change, the recent-time cache ensures that the error logger won't
cause more than one localtime() call per second, no matter how high the
error rate is.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93977 13f79535-47bb-0310-9956-ffa450edef68