Fix singular vertex handling by correctly populating the vertex buffer data.

Also:
- add logic to locate the GUI mel scripts where the binary is located, then default to script search paths
- remove min/max macro defines
- remove iso646.h header (covered by CMake build)
- remove redundant Osd includes
- remove some build warnings
- code style fixes
- build tweak: move the mel scripts to the correct location in the build area

fixes #239