Reviewed by Darin, Dave and Trey, and given the seal of approval by Don.

	Added a new NSFileManager extension method which can be used to
	remove a file but will refuse to remove a directory. Used it
	wherever we remove files but not directories.

        * Misc.subproj/WebNSFileManagerExtras.h:
        * Misc.subproj/WebNSFileManagerExtras.m:
	(-[NSFileManager _web_removeFileOnlyAtPath:]): New method that
	removes a file using unlink(2), which means we can't possibly remove a directory.
	Also unlink ._ file if we are on a filesystem that doesn't support a resource fork.
        * Database.subproj/WebFileDatabase.m:
        (-[WebFileDatabase _truncateToSizeLimit:]):  Use the new method.
        (-[WebFileDatabase performRemoveObjectForKey:]): Use the new method.

WebKit:

        Reviewed by Darin, Dave and Trey, and given the seal of approval by Don.

	Use new safer file removal call that does not handle directories.

        * Downloads.subproj/WebDownloadHandler.m:
	(-[WebDownloadHandler cleanUpAfterFailure]): Use
	_web_removeFileOnlyAtPath:
        * Plugins.subproj/WebBaseNetscapePluginStream.m:
        (-[WebBaseNetscapePluginStream dealloc]): Use _web_removeFileOnlyAtPath:
        (-[WebBaseNetscapePluginStream finishedLoadingWithData:]): Use _web_removeFileOnlyAtPath:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@3324 268f45cc-cd09-0410-ab3c-d52691b4dbfc