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-ifchange.py

@@ -1,66 +0,0 @@
-#!/usr/bin/env python2
-import os, sys, traceback
-
-import vars_init
-vars_init.init(sys.argv[1:])
-
-import vars, state, builder, jwack, deps
-from logs import debug2, err
-
-def should_build(t):
-    f = state.File(name=t)
-    if f.is_failed():
-        raise builder.ImmediateReturn(32)
-    dirty = deps.isdirty(f, depth='', max_changed=vars.RUNID,
-                         already_checked=[])
-    return f.is_generated, dirty == [f] and deps.DIRTY or dirty
-
-
-def main():
-    rv = 202
-    try:
-        if vars_init.is_toplevel and vars.LOG:
-            builder.close_stdin()
-            builder.start_stdin_log_reader(
-                status=True, details=True,
-                pretty=True, color=True, debug_locks=False, debug_pids=False)
-        if vars.TARGET and not vars.UNLOCKED:
-            me = os.path.join(vars.STARTDIR,
-                              os.path.join(vars.PWD, vars.TARGET))
-            f = state.File(name=me)
-            debug2('TARGET: %r %r %r\n'
-                   % (vars.STARTDIR, vars.PWD, vars.TARGET))
-        else:
-            f = me = None
-            debug2('redo-ifchange: not adding depends.\n')
-        jwack.setup(1)
-        try:
-            targets = sys.argv[1:]
-            if f:
-                for t in targets:
-                    f.add_dep('m', t)
-                f.save()
-                state.commit()
-            rv = builder.main(targets, should_build)
-        finally:
-            try:
-                state.rollback()
-            finally:
-                try:
-                    jwack.force_return_tokens()
-                except Exception, e:  # pylint: disable=broad-except
-                    traceback.print_exc(100, sys.stderr)
-                    err('unexpected error: %r\n' % e)
-                    rv = 1
-    except KeyboardInterrupt:
-        if vars_init.is_toplevel:
-            builder.await_log_reader()
-        sys.exit(200)
-    state.commit()
-    if vars_init.is_toplevel:
-        builder.await_log_reader()
-    sys.exit(rv)
-
-
-if __name__ == '__main__':
-    main()