Specialize args LOGGER, LOG-FUNC on T to eliminate unused warnings.

Eliminates warnings before this change that look something like

;Compiler warnings for "home:lisp;quicklisp;local-projects;log4cl;src;appender-base.lisp.newest" :
;   In (APPENDER-DO-APPEND :AROUND (APPENDER T T T)) inside an anonymous lambda form: Unused lexical variable LOGGER
;   In (APPENDER-DO-APPEND :AROUND (APPENDER T T T)) inside an anonymous lambda form: Unused lexical variable LOG-FUNC
; Warning: Lisp compilation had style-warnings while compiling #<CL-SOURCE-FILE "log4cl" "src" "appender-base">