Fix log() output so you can cut-and-paste it verbatim into a command line.

It used to say:
	redo:   t/all
	redo:     hello
and now it says:
	redo    t/all
	redo      t/hello

ie. there's no colon, and the path is intact.  That means if the build
fails, you can cut-and-paste 'redo   t/hello', add a -v, and try to debug
what went wrong.

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
+STARTDIR = os.environ.get('REDO_STARTDIR', '')
 BASE = os.environ.get('REDO_BASE', '')
 if BASE:
     BASE = os.path.abspath(BASE)