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/vars_init.py

@@ -0,0 +1,53 @@
+import sys, os
+
+
+is_toplevel = False
+
+
+def init_no_state():
+    global is_toplevel
+    if not os.environ.get('REDO'):
+        os.environ['REDO'] = 'NOT_DEFINED'
+        is_toplevel = True
+    if not os.environ.get('REDO_BASE'):
+        os.environ['REDO_BASE'] = 'NOT_DEFINED'
+
+
+def init(targets):
+    global is_toplevel
+    if not os.environ.get('REDO'):
+        # toplevel call to redo
+        is_toplevel = True
+        if len(targets) == 0:
+            targets.append('all')
+        exenames = [os.path.abspath(sys.argv[0]),
+                    os.path.realpath(sys.argv[0])]
+        dirnames = [os.path.dirname(p) for p in exenames]
+        trynames = ([os.path.abspath(p+'/../lib/redo') for p in dirnames] +
+                    [p+'/../redo' for p in dirnames] +
+                    dirnames)
+        seen = {}
+        dirs = []
+        for k in trynames:
+            if not seen.get(k):
+                seen[k] = 1
+                dirs.append(k)
+        os.environ['PATH'] = ':'.join(dirs) + ':' + os.environ['PATH']
+        os.environ['REDO'] = os.path.abspath(sys.argv[0])
+
+    if not os.environ.get('REDO_BASE'):
+        base = os.path.commonprefix([os.path.abspath(os.path.dirname(t))
+                                     for t in targets] + [os.getcwd()])
+        bsplit = base.split('/')
+        for i in range(len(bsplit)-1, 0, -1):
+            newbase = '/'.join(bsplit[:i])
+            if os.path.exists(newbase + '/.redo'):
+                base = newbase
+                break
+        os.environ['REDO_BASE'] = base
+        os.environ['REDO_STARTDIR'] = os.getcwd()
+
+        import state
+        state.init()
+
+    os.environ['REDO_LOCKS'] = os.environ.get('REDO_LOCKS', '')