Made the form instances in the gui variables "private", ie, added an underscore.

Made the form instances in the gui variables "private", ie, added an underscore.
The generated code looks makes more sense, and it may avoid a possible variable collision.

Fixed up variable config to re-read the config file before writing,
so 2 or more variables using the same config file cant "fight".

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@11284 221aa14e-8319-0410-a670-987f0aec2ac5