Pass the /d2Zi+ flag to the compiler to get better debug support for optimized builds

http://randomascii.wordpress.com/2013/09/11/debugging-optimized-codenew-in-visual-studio-2012/

Inspired by TortoiseSVN rev. 25277.

Signed-off-by: Sven Strickroth <email@cs-ware.de>