Fixed build against 3.1.x
From Martin Naylor, "Fix for VS2010+ when compiling VPB."
Fixed warning
From Ruben Smelik, "I’ve tried VPB for the first time this week (for the visualization of a high-resolution areal dataset), and I’m very enthusiastic about it: it just works and is very fast!
During this, I’ve spotted a small error in Commandline.cpp, the output bounds (“-b”) are not handled correctly if ymin > ymax (e.g. as in UTM North coordinates). Attached is the fix (against svn trunk version)."