Fix file modes, removing and adding executable permissions

*.dmg, *.gz, *.sig files don't really have any business being marked
executable. *.sh files are intended to be executed, and adding
executable modes to the Windows binaries is helpful when cloning the
repository under Cygwin (where if the *.exe does NOT have an
executable mode set, Windows is unable to launch it).
Merge pull request #13 from chungy/master

Fix file modes, removing and adding executable permissions