the following flags are recognized by the new shell (/bin/sh):
'--':	only as zero-th arg, means that this was spawned by login
	and hence accounting should be done on exit.  also, no '>'
	is preprended to the '&' prompt.
'-p!':	changes preprompt char from '>' to '!' .
'-p ++': sets prompt for shell to be '++' .
'-a fl': file 'fl' is executed as an autostart
	before prompting the standard input for commands.
'-e':	echoes the command to the standard output immediately
	before executing (useful for debugging command files).
'-c cmd': executes the string 'cmd' as though it had been typed directly
	to the shell, and then returns.
'-t':	reads one line from the standard input, executes
	the specified command, and then returns ('-c' is
	generally preferred, if possible).
