Make MtProtoSender not thread-safe
Make MtProtoSender not thread-safe

Rationale: a new connection should be spawned if one desires to
send and receive requests in parallel, which would otherwise cause
one of either threads to lock.

expectocode/Telethon,LonamiWebs/Telethon,LonamiWebs/Telethon,LonamiWebs/Telethon,andr-04/Telethon,LonamiWebs/Telethon