Support Visual Studio as a compiler platform.

Aside from variable definition order changes, the biggest changes to support Visual Studio is that __func__ is supported by Visual Studio so a macro had to be made to allow for __FUNCTION__ in cases where Visual Studio is used (I couldn't find an nginx version). Visual Studio also has issues with the variatic version of ngx_log_debug, so I had to switch them out for the versions that specify parameter count.

This was tested with VS 2010 which is the latest that nginx recommends on their website. Other versions are likely to work as well.