14/11/96	started12/12/96	first mostly working version13/12/96	fixed bug in builtin_if14/12/96	prompt fixed, dup fixed.17/1/97		fiddled with shell script perm checking16/2/97		converted to yacc grammar18/2/97		got pipes and backquotes working, with only minor hacks...2/4/00		revamped:			single process, single main module; added load builtin; added ${} operator;			added eval and std modules17/4/00		added '=' and ':=' operators; removed builtin 'set' and 'local'.11/6/00		added tuple assignment2/3/01		added n-char lookahead in lexer; ':' no longer so special15/2/01		store environment variables in standard quoted format.