[setup] check if darwin

AUTHORS.txt

@@ -1,3 +1 @@
-# This list was out of date, I've put "see contributors" for the moment. Not sure how to fix long term but don't want to be 
-# embarrassed by some off the great contributors of late being omitted from a list.
 See contributors.

setup.py

@@ -26,11 +26,7 @@ del version_dummy
 #Mac OS X Clang doesn't support OpenMP at the current time.
 #This detects if we are building on a Mac
 def ismac():
-    platform = sys.platform
+    return sys.platform[:6] == 'darwin'
-    ismac = False
-    if platform[:6] == 'darwin':
-        ismac = True
-    return ismac
 
 if ismac():
     compile_flags = [ '-O3', ]