14/11/96	started
12/12/96	first mostly working version
13/12/96	fixed bug in builtin_if
14/12/96	prompt fixed, dup fixed.
17/1/97		fiddled with shell script perm checking
16/2/97		converted to yacc grammar
18/2/97		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 modules
17/4/00		added '=' and ':=' operators; removed builtin 'set' and 'local'.
11/6/00		added tuple assignment
2/3/01		added n-char lookahead in lexer; ':' no longer so special
15/2/01		store environment variables in standard quoted format.
