Use array storage for line-editing globals, rather then store heap pointers
Use array storage for line-editing globals, rather then store heap pointers

The getstring() function provides temporary pointers to atoms in the
prolog heap. The previous code for the history_file and prompt strings
saved the atom pointers indefinitely leading to errors when the heap
changes due to garbage collection. Fixes #99

AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog