[Gtkradiant] Crash fix patches for trunk

[Nerius Landys]

I'll put my two cents in for the issues that I reported (hi I'm
Rambetter).  Just so you know, I've already tested these fixes and
they indeed fix the 2 problems below.  Keep reading, comments in-line.

> [Linux] Fix crash and data loss when saving shader, report by Rambetter.
> http://github.com/mfn/GtkRadiant/commit/625a42c77551351f5821468351b9d6ef2bb41a24.diff

Steps to reproduce: In Linux, open a shader file, have some shaders
appear in the texture selection window.  Shift+click on a texture with
a shader.  This opens a text editor window with the contents of the
shader file.  Hitting "Save" on this window would cause a segfault in
Radiant, and the shader file would be truncated to zero length
!!!!!!!!!  Terrible for n00bs to deal with this bug!

> [Linux] Fix attempt: models with upper case letters in the path are not
> shown, reported by Rambetter.
> http://github.com/mfn/GtkRadiant/commit/4ae38a57e61bda27e99d75001400892931c28c62.diff

The very last paragraph of this URL describes the problem with
CAPITALIZATION in .md3 model paths:
http://daffy.nerius.com/radiant/#appx-models