Make http::client::make_request() abortable

[xemul]

Currently the method can block in one of 4 places:

• connecting to server
• waiting for a connection from pool
• writing request to socket
• reading response from server

Either of the steps should be abortable. One of the use-cases is to time-out the request (see #2304). Another -- abort of large file upload in case this upload by user request (e.g. cancelling backup process for whatever reason)