mod_storage_appendmap: Fix keyvalue writes store_raw() takes a filename, unlike most other datamanager functions that take a series of path components, leading to this bug where it would write the hostname into a file named after the first argument (commonly a username) in the working directory.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```