hgweb: be sure to drain request data even in early error conditions Thanks to Mads Kiilerich with noticing this. The hg client can only read data after all the sent data has been read, so we have to read all the request data even if we're not going to do anything with it (in error conditions). This is not easy to fix in the client, because we're using Python's httplib, which is strictly stateful. Abstracted the draining into a separate method.