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.py

@@ -0,0 +1,46 @@
+import os
+from atoi import atoi
+
+if not os.environ.get('REDO'):
+    import sys
+    sys.stderr.write('%s: error: must be run from inside a .do\n'
+                     % sys.argv[0])
+    sys.exit(100)
+
+PWD = os.environ.get('REDO_PWD', '')
+TARGET = os.environ.get('REDO_TARGET', '')
+DEPTH = os.environ.get('REDO_DEPTH', '')
+DEBUG = atoi(os.environ.get('REDO_DEBUG', ''))
+DEBUG_LOCKS = os.environ.get('REDO_DEBUG_LOCKS', '') and 1 or 0
+DEBUG_PIDS = os.environ.get('REDO_DEBUG_PIDS', '') and 1 or 0
+VERBOSE = os.environ.get('REDO_VERBOSE', '') and 1 or 0
+XTRACE = os.environ.get('REDO_XTRACE', '') and 1 or 0
+KEEP_GOING = os.environ.get('REDO_KEEP_GOING', '') and 1 or 0
+LOG = atoi(os.environ.get('REDO_LOG', '1'))  # defaults on
+LOG_INODE = os.environ.get('REDO_LOG_INODE', '')
+COLOR = atoi(os.environ.get('REDO_COLOR', '1'))  # defaults on
+# subprocesses mustn't pretty-print if a parent is running redo-log
+PRETTY = (not LOG) and atoi(os.environ.get('REDO_PRETTY', '1'))
+SHUFFLE = os.environ.get('REDO_SHUFFLE', '') and 1 or 0
+STARTDIR = os.environ.get('REDO_STARTDIR', '')
+RUNID = atoi(os.environ.get('REDO_RUNID')) or None
+BASE = os.environ['REDO_BASE']
+while BASE and BASE.endswith('/'):
+    BASE = BASE[:-1]
+
+UNLOCKED = os.environ.get('REDO_UNLOCKED', '') and 1 or 0
+os.environ['REDO_UNLOCKED'] = ''  # not inheritable by subprocesses
+
+NO_OOB = os.environ.get('REDO_NO_OOB', '') and 1 or 0
+os.environ['REDO_NO_OOB'] = ''    # not inheritable by subprocesses
+
+
+def get_locks():
+    """Get the list of held locks."""
+    return os.environ.get('REDO_LOCKS', '').split(':')
+
+def add_lock(name):
+    """Add a lock to the list of held locks."""
+    locks = set(get_locks())
+    locks.add(name)
+    os.environ['REDO_LOCKS'] = ':'.join(list(locks))