Document the addition of certificate pairs.

 Changes between 0.9.7 and 0.9.8  [xx XXX 2002]

  *) Add the ASN.1 structures and functions for CertificatePair, which

     is defined as follows (according to X.509_4thEditionDraftV6.pdf):

     CertificatePair ::= SEQUENCE {

	forward		[0]	Certificate OPTIONAL,

	reverse		[1]	Certificate OPTIONAL,

	-- at least one of the pair shall be present -- }

     Also implement the PEM functions to read and write certificate

     pairs, and defined the PEM tag as "CERTIFICATE PAIR".

     This needed to be defined, mostly for the sake of the LDAP

     attribute crossCertificatePair, but may prove useful elsewhere as

     well.

     [Richard Levitte]

  *) Make it possible to inhibit symlinking of shared libraries in

     Makefile.shared, for Cygwin's sake.

     [Richard Levitte]