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'.

docs/cookbook/latex/default.runtex.do

@@ -0,0 +1,58 @@
+# latex produces log output on stdout, which is
+# not really correct.  Send it to stderr instead.
+exec >&2
+
+# We depend on both the .latex file and its .deps
+# file (which lists additional dependencies)
+redo-ifchange "$2.latex" "$2.deps"
+
+# Next, we have to depend on each dependency in
+# the .deps file.
+cat "$2.deps" | xargs redo-ifchange
+
+tmp="$2.tmp"
+rm -rf "$tmp"
+mkdir -p "$tmp"
+
+# latex generates eg.  the table of contents by
+# using a list of references ($2.aux) generated
+# during its run.  The first time, the table of
+# contents is empty, so we have to run again. 
+# But then the table of contents is non-empty,
+# which might cause page numbers to change, and
+# so on.  So we have to keep re-running until it
+# finally stops changing.
+touch "$tmp/$2.aux.old"
+ok=
+for i in $(seq 5); do
+    latex --halt-on-error \
+        --output-directory="$tmp" \
+        --recorder \
+        "$2.latex" </dev/null
+    if diff "$tmp/$2.aux.old" \
+            "$tmp/$2.aux" >/dev/null; then
+        # .aux file converged, so we're done
+        ok=1
+        break
+    fi
+    echo
+    echo "$0: $2.aux changed: try again (try #$i)"
+    echo
+    cp "$tmp/$2.aux" "$tmp/$2.aux.old"
+done
+
+if [ "$ok" = "" ]; then
+    echo "$0: fatal: $2.aux did not converge!"
+    exit 10
+fi
+
+# If the newly produced .dvi disappears, we need
+# to redo.
+redo-ifchange "$tmp/$2.dvi"
+
+# With --recorder, latex produces a list of files
+# it used during its run.  Let's depend on all of
+# them, so if they ever change, we'll redo.
+grep ^INPUT "$tmp/$2.fls" |
+    cut -d' ' -f2 |
+    xargs redo-ifchange