imm32: Have both ImmInternalPostIMEMessage and ImmInternalSendIMENotify receive an InputContextData parameter instead of relaying on root_context.

This works for direct connections but in case of proxy connections server
port and host port usually are different.

HTTP_DealWithProxy replaces the request path with a full URL to make sure
a correct request is built for for the proxy. This will work just once in
case of a redirect because the path will be appended to the redirect url,
resulting in an incorrect url.

Based on a patch by Mike Hearn.