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'.

bin/default.do

@@ -0,0 +1,33 @@
+exec >&2
+
+case $1 in
+	redo-sh)
+		redo-ifchange ../redo/sh
+		cat >$3 <<-EOF
+			#!/bin/sh
+			d=\$(dirname "\$0")/..
+			[ -x \$d/lib/redo/sh ] && exec \$d/lib/redo/sh "\$@"
+			[ -x \$d/redo/sh ] && exec \$d/redo/sh "\$@"
+			echo "\$0: fatal: can't find \$d/lib/redo/sh or \$d/redo/sh" >&2
+			exit 98
+		EOF
+		chmod a+x "$3"
+		;;
+	redo|redo-*)
+		redo-ifchange ../redo/whichpython
+		read py <../redo/whichpython
+		cmd=${1#redo-}
+		cat >$3 <<-EOF
+			#!$py -S
+			import sys, os;
+			exe = os.path.realpath(os.path.abspath(sys.argv[0]))
+			exedir = os.path.dirname(exe)
+			sys.path.insert(0, os.path.join(exedir, '../lib'))
+			sys.path.insert(0, os.path.join(exedir, '..'))
+			import redo.cmd_$cmd
+			redo.cmd_$cmd.main()
+		EOF
+		chmod a+x "$3"
+		;;
+	*) echo "$0: don't know how to build '$1'" >&2; exit 99 ;;
+esac