libcurl: security bump to version 7.40.0

Fixes:
CVE-2014-8150 - When libcurl sends a request to a server via a HTTP
proxy, it copies the entire URL into the request and sends if off.
If the given URL contains line feeds and carriage returns those will be
sent along to the proxy too, which allows the program to for example
send a separate HTTP request injected embedded in the URL.

CVE-2014-8151 - libcurl stores TLS Session IDs in its associated Session
ID cache when it connects to TLS servers. In subsequent connects it
re-uses the entry in the cache to resume the TLS connection faster than
when doing a full TLS handshake. The actual implementation for the
Session ID caching varies depending on the underlying TLS backend.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>