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-stamp.py

@@ -1,60 +0,0 @@
-#!/usr/bin/env python2
-import sys, os
-import vars, state
-from logs import err, debug2
-
-
-def main():
-    if len(sys.argv) > 1:
-        err('%s: no arguments expected.\n' % sys.argv[0])
-        sys.exit(1)
-
-    if os.isatty(0):
-        err('%s: you must provide the data to stamp on stdin\n' % sys.argv[0])
-        sys.exit(1)
-
-    # hashlib is only available in python 2.5 or higher, but the 'sha'
-    # module produces a DeprecationWarning in python 2.6 or higher.  We want
-    # to support python 2.4 and above without any stupid warnings, so let's
-    # try using hashlib first, and downgrade if it fails.
-    try:
-        import hashlib
-    except ImportError:
-        import sha
-        sh = sha.sha()
-    else:
-        sh = hashlib.sha1()
-
-    while 1:
-        b = os.read(0, 4096)
-        sh.update(b)
-        if not b:
-            break
-
-    csum = sh.hexdigest()
-
-    if not vars.TARGET:
-        sys.exit(0)
-
-    me = os.path.join(vars.STARTDIR,
-                      os.path.join(vars.PWD, vars.TARGET))
-    f = state.File(name=me)
-    changed = (csum != f.csum)
-    debug2('%s: old = %s\n' % (f.name, f.csum))
-    debug2('%s: sum = %s (%s)\n' % (f.name, csum,
-                                    changed and 'changed' or 'unchanged'))
-    f.is_generated = True
-    f.is_override = False
-    f.failed_runid = None
-    if changed:
-        f.set_changed()  # update_stamp might skip this if mtime is identical
-        f.csum = csum
-    else:
-        # unchanged
-        f.set_checked()
-    f.save()
-    state.commit()
-
-
-if __name__ == '__main__':
-    main()