By default, when discovering files for users, we use the filename
patterns to determine whether or not we should check that file. However,
when a user provides the path to a file, we should instead skip checking
the name against the filename patterns provided.

For example, in Flake8 2.6 this worked:

    $ flake8 bin/script.py
    $ flake8 bin/script

But prior to this commit only

    $ flake8 bin/script.py

works. This commit will skip the filename pattern check if the user
provides the path explicitly which allows

    $ flake8 bin/script

to work again as expected.

Closes #266