libcurl: security bump to version 7.42.0

Fixes:
CVE-2015-3144 - host name out of boundary memory access
CVE-2015-3145 - cookie parser out of boundary memory access
CVE-2015-3148 - Negotiate not treated as connection-oriented
CVE-2015-3143 - Re-using authenticated connection when unauthenticated

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