Attention, Visual C++ support developers and fans

[KJK::Hyperion]

I forgot to add to the commit message for r41520 that I lowered the
warning level of Visual C++ from -Wall to -W1. This will let us fix the
most serious compatibility issues first. Remember: set ROS_RBUILDFLAGS
to -dd -Mcmsc, and make --keep-going is your friend. Now go, and make
awesome things with this!