VS POSIX deprecation & VS2010 solution tweaking

Conditional defines should handle Windows POSIX deprecated functions
better (cf
http://msdn.microsoft.com/fr-fr/library/ms235384(v=vs.90).aspx)
VS2010 project configuration tweaking, disabled Security-enhanced
functions warning (cf
http://msdn.microsoft.com/fr-fr/library/8ef0s5kh(v=vs.90).aspx), warning
level set to W3 for Release configuration, removed unneeded main.c from
dfu-util project compilation process