desktop.el: Add frames and windows configuration save&restore

[Jérémy Compostella]

All,

The attached patch provides the desktop frame and windows configuration
save&restore feature : the desktop module saves all the frame and their
respective windows configuration. On the next Emacs session, after
having restored all the buffers, the desktop module will then restore
all the frame with their window configuration.

This patch probably fits the following TODO item:

 ** Make desktop.el save the "frame configuration" of Emacs (in some
    useful sense).

I have tried to make this feature as customizable as possible:
- This feature is disabled by default with the customizable
  `desktop-save-frames' in order to keep the current behavior for users
  whose could not want this.
- The `desktop-save-selected-frame-only' force the frame and window
  configuration of the current frame only.
- The saved frame parameters is customizable through
  `desktop-frame-parameters-to-save'.
- The saved window properties is customizable through
  `desktop-window-properties-to-save'.

First, I was trying to implement this feature in one of my own Emacs
module but talking with other Emacs users around me I figured out that,
first, this feature is probably expected, and second, it should be
provided by the desktop package.

I've tried to write the best code I could but it's my first "important"
patch to this project and I will be happy to take all your remark into
account ;)

Best regards,

Jérémy

0001-desktop.el-Add-frames-and-windows-configuration-save.patch
Description: 0001-desktop.el-Add-frames-and-windows-configuration-save.patch