Add missing libraries to the Windows GTK+ bundle.

Either libgcc_s_dw2 or libgcc_s_seh is now included in the bundle depending on the bitness. Since libwinpthread is also included in the bundle, these three libraries are not copied anymore to the installation root in order to provide the required dependencies for libssp. These dependencies are now provided by the GTK+ bundle, which needs these libraries anyway.
Some fixes for the website.

* Reference to the formatting of the IRC channel website has been moved to the next release section.
* Current release section has been reverted to suppression rather than formatting of the IRC channel website.
* Other small source code fixes.