Detach verify thread from NSPR on linux.
Detach verify thread from NSPR on linux.

The threads in our thread pool terminate after we have called
PR_Cleanup.  Unless we detach them from NSPR, if we use
CertVerifier, net_unittests dies with segfault on shutdown.

BUG=10911
TEST=net_unittests passes with code that uses CertVerifier.

Review URL: http://codereview.chromium.org/115856

git-svn-id: http://src.chromium.org/svn/trunk/src@17160 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 782c20baf9d12e8eacda6cc6381af6261d596b09
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser