Fixed|Partitioner: Compiler error (global variable shadowing)

The static validCount in partitioner.cpp was shadowed by the global
variable of the same name, with C-linkage, in render/r_main.h when
building with MSVC (at least). Resulting in holes around one-way
window hack constructs in some maps.
Fixed: Build failure (missing header, GL def, Qt 4.8 fund)

Included missing <QSet>, defined the GLES 2 specific
GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS, and replaced
QImage::fill(QColor) with a Qt 4.7 compatible call.