asterisk:
 * disable "optimize asterisk for low-memory usage"-option by default as it is [http://www.ip-phone-forum.de/showthread.php?t=266864&p=1984050&viewfull=1#post1984050 known] to cause problems with some modules
 * add corresponding menuconfig-help-entry
 * refs #706


git-svn-id: file:///var/svn/freetz/trunk@11644 149334a1-2f27-0410-a3b9-fc62619ac1e6