Don't use variable_set to store runtime data

Problem/Motivation

Currently moopapi_wrap(), which is only called by moopapi_init(), uses variable_set() to store, as far as I can tell, temporary runtime information.
This is a bad idea because variable_set() triggers a write to the DB as well as cache_clear_all('variables', 'cache_bootstrap');.
This has an unnecessary negative performance impact.

Proposed resolution

Simply use the global $conf array to temporarily adjust / overwrite the stored configuration.

Remaining tasks

Reviews needed.

User interface changes

None

API changes

None