return a list of uncovered files, not uncovered dirs

Change the OWNERS check to print files, not directories

Currently, when we run the OWNERS check, we print the list of directories
that contain the relevant OWNERS files for any modified files in a change
still needing approval. 

This has two problems:

1) if we bubble all the way up to the top level OWNERS, we print "" instead of
"src/" or something more useful (bug 157191)

2) for OWNERS files that contain per-file set-noparent entries (like changes to IPC messages), this can be really confusing because an owner of other stuff in the directory might've approved things already.

This change will now print the list of files in the CL that are still unapproved.
This might be a lot more verbose (since you get N lines rather than 1 for N files in a given directory), but hopefully it'll be clearer in the two cases above.

Also, this change takes care of some lingering clean-up in the code to rename some methods to be clearer.

R=maruel@chromium.org
BUG=157191
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=184219

[M-A Ruel, 2013-02-22 14:12:42]

lgtm

[commit-bot: I haz the power, 2013-02-23 00:04:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dpranke@chromium.org/12314044/2001

[commit-bot: I haz the power, 2013-02-23 00:06:40]

Change committed as 184219