memcached-threads: use only one
memcached-threads: use only one

See https://code.google.com/p/modpagespeed/issues/detail?id=672

wanrui/ngx_pagespeed,pagespeed/ngx_pagespeed,digideskio/ngx_pagespeed,wanrui/ngx_pagespeed,0x0mar/ngx_pagespeed,digideskio/ngx_pagespeed,pagespeed/ngx_pagespeed,0x0mar/ngx_pagespeed