Also check if the backup handshake hash should be used on the NSS client

The NSS client auth (as opposed to NSS_PLATFORM_CLIENT_AUTH) also needs
to check if the backup handshake hash should be used.

R=agl@chromium.org,rsleevi@chromium.org
BUG=278370
TEST=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=222724

[wtc, 2013-09-11 21:19:31]

While preparing my backup handshake hash patch for the
NSS upstream, I noticed that Chromium's ssl3_HandleCertificateRequest
also has another code path, used on Linux, that I missed.
This causes Chromium to use SHA-1 in TLS 1.2 client auth
on Linux.

To avoid duplicating code on the two code paths, I created
functions that determines if the backup handshake hash should
be used.

[agl, 2013-09-11 21:37:50]

lgtm

[commit-bot: I haz the power, 2013-09-11 23:06:21]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/wtc@chromium.org/23880010/4001

[commit-bot: I haz the power, 2013-09-12 05:59:36]

Change committed as 222724