Use `diff` command for TFS.

Review Request #7450 — Created June 24, 2015 and submitted — Latest diff uploaded

Information

RBTools
release-0.7.x
c990bc2...

Reviewers

It turns out that difflib's unified diff implementation, while seemingly okay,
chokes pretty badly with files that don't end in newlines, or start with
byte-order markers. After piling workaround on top of workaround, I've decided
to rip it out and just use the diffutils diff command.

Posted some changes containing previously problematic files. Saw that they all
worked.