Description of problem:
When a GnuTLS client uses TLSv1.2, servers which respect client preference for signature methods will select SHA-1 signature for Server Key Exchange message.

Version-Release number of selected component (if applicable):
gnutls-2.8.5-19.el6_7.x86_64

How reproducible:
Always

Steps to Reproduce:
1. tcpdump -i any -s 0 -w capture.pcap -u port 443
2. gnutls-cli --port 443 --priority NORMAL:+VERS-TLS1.2 bugzilla.redhat.com
3. open capture.pcap in wireshark

Actual results:
Client Hello message contains signautre_alorithms extension with following pairs:
SHA1-RSA
SHA1-DSA
SHA256-RSA
SHA384-RSA
SHA512-RSA

The Server Key Exchange message is signed with SHA1-RSA

Expected results:
Extension containing the signature algorithms in following order:
SHA256-RSA
SHA384-RSA
SHA512-RSA
SHA1-RSA
SHA1-DSA

Server Key Exchange signed with SHA256-RSA

Additional info:
This should also affect server side, at the very least when the %SERVER_PRECEDENCE setting is used.