With the current implementation, it is likely to connect/close a socket with...

With the current implementation, it is likely to connect/close a socket with the memcache server for each command sent.
The root cause is a too small idle timeout (600 microseconds).

Add a new directive, 'MemcacheConnTTL',  to control this idle connection timeout with the memcache server(s).
Change the default value from 600 usec (!) to 15 sec as per Yann suggestion.

I've limited accepted values from 1 to 1800 seconds (half an hour) because internaly, the value passed to 'apr_memcache_server_create' is still in mirco-seconds.

PR 58091

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1696105 13f79535-47bb-0310-9956-ffa450edef68