On svn-auth-x509 branch: Resurrect r1614643.

* subversion/include/svn_x509.h
  (svn_x509_certinfo_get_subject,
   svn_x509_certinfo_get_issuer): Clarify in docs that these functions
   return the whole Distinguished Name.
  (svn_x509_certinfo_get_subject_cn): New prototype.
* subversion/libsvn_subr/x509.h
  (svn_x509_certinfo_t): New member subject_cn.
* subversion/libsvn_subr/x509info.c
  (svn_x509_certinfo_dup): Copy the subject_cn.
  (svn_x509_certinfo_get_subject_cn): Implement.
* subversion/libsvn_subr/x509parse.c
  (x509parse_dn_gets): Optionally return the CN in a separate stringbuf.
  (svn_x509_parse_cert): Retreive and return the subject CN.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/svn-auth-x509@1618902 13f79535-47bb-0310-9956-ffa450edef68