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'.

t/.gitignore

@@ -1,3 +1,4 @@
 /broken
 /shellfile
 /stress.log
+/flush-cache

t/101-atime/atime2.do

@@ -1,6 +1,6 @@
 # make sure redo doesn't think merely *reading* the old file counts as
 # modifying it in-place.
 cat $1 >/dev/null 2>/dev/null || true
-./tick
+../../redo/python tick.py
 cat $1 >/dev/null 2>/dev/null || true
 echo hello

t/101-atime/tick.py

@@ -1,4 +1,3 @@
-#!/usr/bin/env python2
 import time
 t2 = int(time.time()) + 1.0
 while 1:

t/130-mode/all.do

@@ -1,5 +1,5 @@
 umask 0022
 redo mode1
-MODE=$(python2 -c 'import os; print oct(os.stat("mode1").st_mode & 07777)')
+MODE=$(../../redo/python -c \
+	'import os; print oct(os.stat("mode1").st_mode & 07777)')
 [ "$MODE" = "0644" ] || exit 78
-

t/all.do

@@ -1,3 +1,5 @@
+redo-ifchange flush-cache
+
 # tests that "set -e" works (.do scripts always run with -e set by default)
 rm -f 000-set-minus-e/log
 redo 000-set-minus-e/all

t/clean.do

@@ -2,5 +2,5 @@
 sed 's/\.do$//' |
 xargs redo
 
-rm -f broken shellfile *~ .*~ stress.log
+rm -f broken shellfile *~ .*~ stress.log flush-cache
 rm -rf 'space home dir'

t/flush-cache.do

@@ -0,0 +1,7 @@
+redo-ifchange ../redo/whichpython $1.in
+read py <../redo/whichpython
+(
+	echo "#!$py"
+	cat $1.in
+) >$3
+chmod a+x $3

t/flush-cache.in

@@ -1,4 +1,3 @@
-#!/usr/bin/env python2
 import sys, os, sqlite3
 
 if "DO_BUILT" in os.environ: