correct AuthConfigFactory.getConfigProvider inconistency in whether layer and appContextID may be null

the version of the javadoc embedded in the 1.0 spec is out of sync with the javadoc
generated from the api src. The javadoc in the spi src is correct and allows these
parameters to be null in the general case. Note that profiles (e.g. the Servlet profile)
establish specific values (and may not allow null values) to be used when implementing
the profile.

Reported to me by Yi Wang.

will be fixed in 1.1, when mifdoclet is re-run to convert javadoc into the mif files that are
included in the framemaker spec document