The newly introduced procedure wiiuse_set_output can be used to set the FILE*
used for each of the loglevels LOGLEVEL_ERROR, LOGLEVEL_WARNING, LOGLEVEL_INFO,
and LOGLEVEL_DEBUG. Setting the logfile to 0 disables log output for a
loglevel. This adds the macro definition WIIUSE_HAS_OUTPUT_REDIRECTION, so
programs can test for the feature.
The internal log macros in definitions.h all honor this output redirection mechanism.
