If the user tries to save a capture file atop a file that has all its

If the user tries to save a capture file atop a file that has all its
write bits turned off or, on 4.4-Lite-based systems, has its "user
immutable" bit turned on, ask them if they really want to overwrite the
file (as those are both used to say "this file is precious, don't let me
easily accidentally trash it") and, if the "user immutable" bit is set,
turn it off first so that the move in the "safe save" won't fail.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@43006 f5534014-38df-0310-8fa8-9805f1628bb7