Raw logs contain @@REDO lines instead of formatted data.

This makes them more reliable to parse.  redo-log can parse each line,
format and print it, then recurse if necessary.  This got a little ugly
because I wanted 'redo --raw-logs' to work, which we want to format the
output nicely, but not call redo-log.

(As a result, --raw-logs has a different meaning to redo and
redo-log, which is kinda dumb.  I should fix that.)

As an added bonus, redo-log now handles indenting of recursive logs, so
if the build was a -> a/b -> a/b/c, and you look at the log for a/b, it
can still start at the top level indentation.

redo.py

@@ -50,7 +50,7 @@ import vars_init
 vars_init.init(targets)
 
 import vars, state, builder, jwack
-from log import warn, err
+from logs import warn, err
 
 try:
     if vars_init.is_toplevel: