php memcache extension: Module 'memcache' already loaded (wheezy)

Part of https://github.com/cargomedia/puppet-packages/issues/439

Output:
```
PHP Warning:  Module 'memcache' already loaded in Unknown on line 0
```

Looks like the config-directory for extensions has changes?
```
$ grep -r 'memcache.so' /etc/php5/
/etc/php5/conf.d/memcache.ini:extension=memcache.so
/etc/php5/mods-available/memcache.ini:extension=memcache.so
```

@ppp0 or @kris-lab please take over