Stop using integer for keys of WrapperObjectCache on Windows

This is because a pointer on Windows can be a Bignum.

Author: mrkn

lib/pycall/wrapper_object_cache.rb

@@ -6,7 +6,12 @@ class WrapperObjectCache
     rescue
       WMAP_SUPPORT_INT_KEY = false
     else
-      WMAP_SUPPORT_INT_KEY = true
+      case RUBY_PLATFORM
+      when /cygwin/, /mingw/, /mswin/
+        WMAP_SUPPORT_INT_KEY = false
+      else
+        WMAP_SUPPORT_INT_KEY = true
+      end
     end
 
     if WMAP_SUPPORT_INT_KEY