Fix include path for build\windows\MSVC-11\Radiant.vcxproj
Add *.opensdf to ignored file.
Rename struct RHOSTSVC to struct radiant_host_services.
Rename struct _RADIANT_ENGINE to struct radiant_engine.
Rename RENGINE to radiant_t.
Prepare to change architecture for returning error for Engine.
Add errno.h
Add RADIANT_E_INARG.
Add RADIANT_E_INVOP.
Rename RADIANT_E_INARG to RADIANT_E_INVAL.