Add a --shuffle option to let you enable dependency randomization.

Previously, for testing, we were *always* randomizing the build order of
dependencies.  That's annoying since it'll make build logs differ randomly
from one run to the next, which could make comparisons harder.  However, the
feature is still useful for uncovering hidden dependencies between objects.

redo.py

@@ -8,6 +8,7 @@ redo [targets...]
 j,jobs=    maximum number of jobs to build at once
 d,debug    print dependency checks as they happen
 v,verbose  print commands as they are run
+shuffle    randomize the build order to find dependency bugs
 """
 o = options.Options('redo', optspec)
 (opt, flags, extra) = o.parse(sys.argv[1:])
@@ -18,6 +19,8 @@ if opt.debug:
     os.environ['REDO_DEBUG'] = '1'
 if opt.verbose:
     os.environ['REDO_VERBOSE'] = '1'
+if opt.shuffle:
+    os.environ['REDO_SHUFFLE'] = '1'
 
 if not os.environ.get('REDO_BASE', ''):
     base = os.path.commonprefix([os.path.abspath(os.path.dirname(t))
@@ -147,7 +150,8 @@ def main():
     retcode = 0
     locked = {}
     waits = {}
-    random.shuffle(targets)  # make it unpredictable for better testing
+    if vars.SHUFFLE:
+        random.shuffle(targets)
     for t in targets:
         if os.path.exists('%s/all.do' % t):
             # t is a directory, but it has a default target

vars.py

@@ -4,6 +4,7 @@ TARGET = os.environ.get('REDO_TARGET', '')
 DEPTH = os.environ.get('REDO_DEPTH', '')
 DEBUG = os.environ.get('REDO_DEBUG', '') and 1 or 0
 VERBOSE = os.environ.get('REDO_VERBOSE', '') and 1 or 0
+SHUFFLE = os.environ.get('REDO_SHUFFLE', '') and 1 or 0
 STARTDIR = os.environ.get('REDO_STARTDIR', '')
 BASE = os.environ.get('REDO_BASE', '')
 if BASE: