Fix stage 2 init: read script from stdin
Fix stage 2 init: read script from stdin

It is now possible to invoke modernish to read a script from standard input,
in the same way you can do with shells. This allows usages like:

	printf '%s\n' "$commands" | modernish

or

	modernish <<'EOF'
	your modernish script here
	EOF

It is also possible to precede the specific shell you want to use to execute
modernish, e.g.:

	printf '%s\n' "$commands" | zsh modernish

	ksh modernish <<'EOF'
	your modernish script here
	EOF

Other tweaks:

- The state of "set -a" is restored at the last possible moment.
- Shell option -e (-o errexit) is explicitly blacklisted.

modernish/modernish