[PATCH] Change the behavior of clang-tidy -checks=, remove -disable-checks.

[Manuel Klimek]

After thinking a bit about this, I'd like to revisit this from scratch (as
it has changed quite a bit).

Why is: -check=<regexp> not enough? Give it a good enough default value
(that is printed if you say -help), and we have the following use cases:
- add something to the default set: clang-tidy -help, copy default set, add
own
- run only a single check: -check=my-full.check
- run only google checks: -check=google-.*

http://reviews.llvm.org/D3770