Support for OpenSSL 1.1.0:

- SRP_VBASE_get_by_user() is deprecated now,
  one should use SRP_VBASE_get1_by_user()
  instead. The new function returns a pointer
  owned by the callee. It must be freed after
  use.

Backport of r1735877 from trunk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x-openssl-1.1.0-compat@1755846 13f79535-47bb-0310-9956-ffa450edef68