Directory reorg: move code into redo/, generate binaries in bin/.

It's time to start preparing for a version of redo that doesn't work
unless we build it first (because it will rely on C modules, and
eventually be rewritten in C altogether).

To get rolling, remove the old-style symlinks to the main programs, and
rename those programs from redo-*.py to redo/cmd_*.py.  We'll also move
all library functions into the redo/ dir, which is a more python-style
naming convention.

Previously, install.do was generating wrappers for installing in
/usr/bin, which extend sys.path and then import+run the right file.
This made "installed" redo work quite differently from running redo
inside its source tree.  Instead, let's always generate the wrappers in
bin/, and not make anything executable except those wrappers.

Since we're generating wrappers anyway, let's actually auto-detect the
right version of python for the running system; distros can't seem to
agree on what to call their python2 binaries (sigh). We'll fill in the
right #! shebang lines.  Since we're doing that, we can stop using
/usr/bin/env, which will a) make things slightly faster, and b) let us
use "python -S", which tells python not to load a bunch of extra crap
we're not using, thus improving startup times.

Annoyingly, we now have to build redo using minimal/do, then run the
tests using bin/redo.  To make this less annoying, we add a toplevel
./do script that knows the right steps, and a Makefile (whee!) for
people who are used to typing 'make' and 'make test' and 'make clean'.

redo/sh.do

@@ -0,0 +1,66 @@
+exec >&2
+redo-ifchange ../t/shelltest.od
+
+rm -rf $1.new
+mkdir $1.new
+
+GOOD=
+WARN=
+
+# Note: list low-functionality, maximally POSIX-like shells before more
+# powerful ones.  We want weaker shells to take precedence, as long as they
+# pass the tests, because weaker shells are more likely to point out when you
+# use some non-portable feature.
+for sh in dash /usr/xpg4/bin/sh ash posh mksh ksh ksh88 ksh93 pdksh \
+		zsh bash busybox /bin/sh; do
+	printf "%-30s" "Testing $sh..."
+	FOUND=`which $sh 2>/dev/null` || { echo "missing"; continue; }
+	
+	# It's important for the file to actually be named 'sh'.  Some
+	# shells (like bash and zsh) only go into POSIX-compatible mode if
+	# they have that name.  If they're not in POSIX-compatible mode,
+	# they'll fail the test.
+	rm -f $1.new/sh
+	ln -s $FOUND $1.new/sh
+	SH=$PWD/$1.new/sh
+	
+	set +e
+	( cd ../t && $SH shelltest.od ) >shelltest.tmp 2>&1
+	RV=$?
+	set -e
+	
+	msgs=
+	crash=
+	while read line; do
+		#echo "line: '$line'" >&2
+		stripw=${line#warning: }
+		stripf=${line#failed: }
+		crash=$line
+		[ "$line" = "$stripw" ] || msgs="$msgs W$stripw"
+		[ "$line" = "$stripf" ] || msgs="$msgs F$stripf"
+	done <shelltest.tmp
+	rm -f shelltest.tmp
+	msgs=${msgs# }
+	crash=${crash##*:}
+	crash=${crash# }
+	
+	case $RV in
+		40) echo "ok $msgs"; [ -n "$GOOD" ] || GOOD=$FOUND ;;
+		41) echo "failed    $msgs" ;;
+		42) echo "warnings  $msgs"; [ -n "$WARN" ] || WARN=$FOUND ;;
+		*)  echo "crash     $crash" ;;
+	esac
+done
+
+rm -rf $1.new $3
+
+if [ -n "$GOOD" ]; then
+	echo "Selected perfect shell: $GOOD"
+	ln -s $GOOD $3
+elif [ -n "$WARN" ]; then
+	echo "Selected mostly good shell: $WARN"
+	ln -s $WARN $3
+else
+	echo "No good shells found!  Maybe install dash, bash, or zsh."
+	exit 13
+fi