Please make .asc files be downloaded instead of displayed

Currently when opening the following link in a browser, the signature will be displayed instead of downloaded: https://www.torproject.org/dist/torbrowser/3.6.5/torbrowser-install-3.6.5_en-US.exe.asc

This can confuse users trying to verify the signature, because they will need the file saved on their disk with most tools. In order to save them a step, and some bewilderment, let's make .asc files be downloaded by browsers.

I believe the Apache configuration snippet to be close to the following:

<FilesMatch "\.asc$">
  ForceType application/octet-stream
  Header set Content-Disposition attachment
</FilesMatch>

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