call SecTrustEvaluate before calling SecTrustGetCertificateCount

SecTrustGetCertificateCount's documentation says SecTrustEvaluate must be called before calling it. Without calling it, SecTrustGetCertificateCount returns 0 in OS X 10.7.
Merge branch '1.x' of github.com:minorblend/AFNetworking into 1.x

# By Indragie Karunaratne (1) and Kevin Cassidy Jr (1)
# Via Mattt Thompson (2) and others
* '1.x' of github.com:minorblend/AFNetworking:
  Same fix as 6c7250e for 1.x branch
  Check CFStringTransform() call for success before using result