setup.py: Add support DragonFlyBSD (closes #77)

Author: Ben Jolitz

setup.py

@@ -256,7 +256,7 @@ def build_extensions(self):
 
         if sys.platform.startswith('linux'):
             self.compiler.add_library('rt')
-        elif sys.platform.startswith('freebsd'):
+        elif sys.platform.startswith(('freebsd', 'dragonfly')):
             self.compiler.add_library('kvm')
         elif sys.platform.startswith('sunos'):
             self.compiler.add_library('kstat')