Fix: Handle non existent directories in ALBA_LIB_PATH correctly

Don't raise a 'Sys_error', just a 'Not_found.

	modified:   ocaml/alba.ml
Added a library table within module table

	modified:   ocaml/module_table.ml
	modified:   ocaml/module_table.mli
Parsing of fully qualified classnames implemented

... but information not yet used.

	modified:   ocaml/ast.ml
	modified:   ocaml/class_table.ml
	modified:   ocaml/class_table.mli
	modified:   ocaml/parser.mly
	modified:   ocaml/support.ml