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/version/gitvars.do

@@ -0,0 +1,28 @@
+redo-ifchange gitvars.pre prodname
+
+read PROD <prodname
+exec >$3
+
+# Fix each line from gitvars.pre where git may or may not have already
+# substituted the variables.  If someone generated a tarball with 'git archive',
+# then the data will have been substituted already.  If we're in a checkout of
+# the git repo, then it won't, but we can just ask git to do the substitutions
+# right now.
+while read line; do
+	# Lines *may* be of the form: $Format: ... $
+	x=${line#\$Format:}  # remove prefix
+	if [ "$x" != "$line" ]; then
+		# git didn't substitute it
+		redo-always   # git this from the git repo
+		x=${x%\$}  # remove trailing $
+		if [ "$x" = "%d" ]; then
+			tag=$(git describe --match="$PROD-*")
+			x="(tag: $tag)"
+		else
+			x=$(git log -1 --pretty=format:"$x")
+		fi
+	fi
+	echo "$x"
+done <gitvars.pre
+
+redo-stamp <$3