Let msvc decide if it needs to re-run the download projects based upon the presence of the downloaded directory.  This now works properly for these targets when it will scroll pass the target as "up-to-date" instead of running it and doing nothing.  This should speed up the build process a bit.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@2371 d0543943-73ff-0310-b7d9-9358b9ac24b2