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-ood.py

@@ -1,45 +0,0 @@
-#!/usr/bin/env python2
-import sys, os
-
-import vars_init
-vars_init.init([])
-
-import vars, state, deps
-from logs import err
-
-if len(sys.argv[1:]) != 0:
-    err('%s: no arguments expected.\n' % sys.argv[0])
-    sys.exit(1)
-
-
-cache = {}
-
-
-def is_checked(f):
-    return cache.get(f.id, 0)
-
-
-def set_checked(f):
-    cache[f.id] = 1
-
-
-def log_override(name):
-    pass
-
-
-def main():
-    cwd = os.getcwd()
-    for f in state.files():
-        if f.is_target():
-            if deps.isdirty(f,
-                            depth='',
-                            max_changed=vars.RUNID,
-                            already_checked=[],
-                            is_checked=is_checked,
-                            set_checked=set_checked,
-                            log_override=log_override):
-                print state.relpath(os.path.join(vars.BASE, f.name), cwd)
-
-
-if __name__ == '__main__':
-    main()