Make rspec-verify and rspec-verify-single dired aware.

* connected with #48
* `rspec-verify` if in the `dired-mode` runs compilation for current directory
* `rspec-verify-single` if in the `dired-mode` buffer runs marked specs or if none marked runs specs under the point. Works with directories too.
* `rspec-verify-single` when in `dired-mode` the compilation will probably fail when `rspec-use-rake-flag` is set. To overcome this more rework on the current code is needed. I wanted to avoid it, kind of.