gschem: add 'page changed' indication. (+patch)

[dmn]

Related: Bug #918265

Currently there is no way to tell whether
active page has changed or not.
I believe, every decent software that deals with
'documents' of some sort, should clearly indicate
to the user what's going on. Can you imagine your
favorite text editor not doing so?
I'm afraid, one can't.

The patch provides that functionality,
adding an asterisk to the main window's title
if current page has modifications.

Please note:
1) If we make changes not via GUI, but,
for example, from guile code, that will not
be reflected.
2) 'Save', 'Save All' menu items and 'Save file'
toolbar button are not reflected either.
I think, they should be disabled if there is
nothing to save.

[Vladimir Zhbanov (vzhbanov)]

Hi, Grom.

I've inadvertently committed your patch. I think now the
indication works wrongly, though it is not your fault, it is fault
of our undo system. So I hope the state we have now will force me
to change it some time.

Thank you for the patch,
  Vladimir

[dmn (graahnul.grom)]

Hi, Vladimir.
Is this the following behaviour you are talking about?

TEST:
- File -> Save
- Perform one action (e.g. delete something)
- Edit -> Undo
RESULT:
page->CHANGED == 1

[dmn (graahnul.grom)]

Reposting patch with proper email address.

[Vladimir Zhbanov (vzhbanov)]

On Sat, Jul 25, 2015 at 11:52:44PM -0000, graahnul.grom wrote:
> Hi, Vladimir.
> Is this the following behaviour you are talking about?
>
> TEST:
> - File -> Save
> - Perform one action (e.g. delete something)
> - Edit -> Undo
> RESULT:
> page->CHANGED == 1

Yes.

Cheers,
  Vladimir