don’t check cache/ in ``nikola check -l``

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
support custom cache folders (does anyone use this?)

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
fix issue number (it’s #1447)

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Merge pull request #1447 from getnikola/ignore-cache-in-check

Don’t check cache/ in ``nikola check -l``