When any of our executables start on Windows create or open a "Wireshark

When any of our executables start on Windows create or open a "Wireshark
is running" mutex. Have the NSIS installer check for this mutex and ask
the user to close Wireshark if it's found. While not perfect this makes
the WinSparkle update process much less annoying.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@47758 f5534014-38df-0310-8fa8-9805f1628bb7