Adding ".Sparkle" to appSupportPath

Problem
------------
finish_installation.app and pkg files will not be removed when we use *.pkg installer and restart system in the installer.

In this case, "Application Support" directory is corrupted by unnecessary pkg files.
We need to scan files under "Application Support" directory and examine whether pkg file or not
in order to remove these pkg files.

It is quite annoying.

Solution
------------
This patch changes location of finish_installation.app and pkg files to
"~/Library/Application Support/APPNAME/.Sparkle".

pkg file will be downloaded into
"~/Library/Application Support/APPNAME/.Sparkle/APPNAME VERSION/APPNAME.pkg".

Then, we can remove finish_installation.app and pkg files certainly by removing
"~/Library/Application Support/APPNAME/.Sparkle".