[FIX] base: binary url attachment on windows

On windows when opening a binary file a 'b' flag is to be used:
 https://docs.python.org/2/tutorial/inputoutput.html#reading-and-writing-files

Before this commit, /web/image/* and /web/content/* routes serving
an ir.attachment with url could return empty or truncated content.

opw-693306

openerp/addons/base/ir/ir_http.py

@@ -264,7 +264,7 @@ class ir_http(osv.AbstractModel):
                     module_path = os.path.join(os.path.normpath(module_path), '')  # join ensures the path ends with '/'
                     module_resource_path = os.path.normpath(module_resource_path)
                     if module_resource_path.startswith(module_path):
-                        with open(module_resource_path, 'r') as f:
+                        with open(module_resource_path, 'rb') as f:
                             content = base64.b64encode(f.read())
                         last_update = str(os.path.getmtime(module_resource_path))