[Nano-devel] [RFC] add toggle to writeout selection instead of entire buffer

[Brand Huntsman]

When a selection is active, ^O defaults to writing the selection to a new file. 
Comment/uncomment, indent/unindent, search&replace, piping selection to command 
and so on can all leave a selection active after performing them. This is great 
when performing multiple tasks on the same selection. But rapidly pressing ^O 
and ENTER (muscle memory) to save, results in a still modified unsaved buffer.

I propose ^O only saves the selection if a toggle is used, something like ^O^S. 
Anyone wanting to save a selection must type out the filename and an extra ^S 
won't interrupt their workflow much, especially for a feature that is probably 
rarely used. Everyone saves files and needing to unselect before saving 
disrupts normal workflow and can lead to unsaved files (if you don't notice and 
walk away from the computer).

I also propose changing the prompt to reflect what is being saved.

"File Name to Write:" ->
"File Name to Write [Entire Buffer]:"

"Write Selection to File:" ->
"File Name to Write [Selection]:"

Displaying [Buffer] or [Entire Buffer] will help indicate the selection won't 
be written, for anyone who expected it. Enabling ^S will clear the filename and 
disabling it will restore to the buffer's filename.