add: MAKE-APROPOS-MATCHER is now a part of the interface.

* moved from function in swank.lisp to DEFINTERFACE in swank-backend.lisp
add: *SLDB-PRINT-CASE* makes prettier debugger backtrace frames
Add: add regexp-capable MAKE-APROPOS-MATCHER implementation for allegro
add: look for .swank.lisp in HOME envvar before trying USER-HOME-DIR-PATHNAME
fix: use allegro's CG:*DEFAULT-CG-BINDINGS* for repl threads when available