Prepare for memcached builds

In theory, this should work, but in practice it fails since libmemcached
ships headers with standard names[1] which are erroneously included.  We
still make the change, if only as a reminder that libmemcached needs to
be fixed.

We shall have a look at building with `--enable-memcached-igbinary` when
the header issue has been resolved.

[1] <awesomized/libmemcached#61 (comment)>

data/config/pecl/exts.ini

@@ -500,13 +500,14 @@ ignore=1
 [pdo_informix]
 ignore=1
 
-; actually this wont work, the only port i could find is 0.29, but the ext require 1.x
 [memcached]
-ignore=1
-type=with
+type=enable
 libs[]=libmemcached
-exts[]=
-opts[]=
+opts[]=--enable-memcached=shared
+opts[]=--enable-memcached-session
+opts[]=--disable-memcached-igbinary
+opts[]=--enable-memcached-json
+no_conf=1
 
 [v8js]
 type=with