Remove circular depency in Log::Log4perl::Appender

[lharey]

only require Log::Log4perl::Config if it hasn't already been loaded

Refs #59

[kgoess]

Mike, fwiw, Class::Load is not in core:

$ corelist Class::Load

Data for 2014-01-09
Class::Load was not in CORE (or so I think)

[mschilli]

Good catch, Kevin! Lisa, I forgot to mention that Log4perl doesn't use external dependencies, so Class::Load isn't going to work, but I think you can examine %INC to see if a class has already been loaded.