Allow trivial-validate.py to validate single file

If the first argument to trivial-validate is an existing file,
then only run validation tests on that file. Optionally, specify
a directory in which to check for duplicates of this file.
Ex: python trivial-validate.py <filename> <rulesets-directory-name>

Otherwise, if the argument is a directory, default to previous
behavior.
don't chdir if there is only one file to test
Merge branch '3.0' of git://git.torproject.org/git/https-everywhere into 3.0
[Dell] mixed content; also linux.dell.com redirects to http

https://trac.torproject.org/projects/tor/ticket/8569
Merge remote-tracking branch 'upstream/3.0' into 3.0
[Bahn.de] Switch to enumerated subdomains.

https://trac.torproject.org/projects/tor/ticket/8489
[GoogleMaps] exclude http://maps.google.com/local_url

https://trac.torproject.org/projects/tor/ticket/8652
https://trac.torproject.org/projects/tor/ticket/8627
Merge remote-tracking branch 'upstream/3.0' into 3.0
Disable https for Cloudfront services on Droplr

As reported in https://trac.torproject.org/projects/tor/ticket/8572,
some Droplr content does not display with the Cloudfront rule.