Added !SSPI to the features list of the HTTP digest tests, as SSPI
based builds now use the Windows SSPI messaging API rather than the
internal functions, and we can't control the random numbers that get
used as part of the digest.
When allowing NTLM, the re-use connection logic was too focused on
finding an existing NTLM connection to use and didn't properly allow
re-use of other ones. This made the logic not re-use perfectly re-usable
connections.
Added test case 1418 and 1419 to verify.
Regression brought in 8ae35102c (curl 7.35.0)
Reported-by: Jeff King
Bug: http://thread.gmane.org/gmane.comp.version-control.git/242213