CMake project reloading.

[Olivier J. G.]

> BTW I didn't get to reproduce your problem, if you can provide me the bt or
> a way to reproduce it that would be really nice. I actually cannot.

I did provide reproduction instructions in the first email. Basically
just select a header and cpp in a CMake project and "Remove Files".
That's assuming the cpp get deleted first in the loop, but in practice
it always does for me.

Anyhow, to wrap this episode up. I would say that to truly fix this,
the following rules would apply:

If a ProjectItem hasn't been removed, it should always be available,
and if it has been removed, it shouldn't crash.

Reference counting would accomplish both of these.

I had also thought that it would be nice if, to avoid the reload
process where you often lose access to your project for 5-10 seconds
at a time, the following could be done:

RemoveFiles/Folders instead of File/Folder, so multiple deletions only
require one reread.
Perhaps creating a temporary model for a reload to be processed under,
so life can go on during a CMakeLists re-read.

@Aleix: are you the one who does the CMake stuff? If so, do you think
this is workable?

-Olivier JG