cmake: Document GSSAPI_FLAVOR_MIT and GSSAPI_FLAVOR_HEIMDAL.
cmake: Document GSSAPI_FLAVOR_MIT and GSSAPI_FLAVOR_HEIMDAL.

pouete/libssh,pouete/libssh,robxu9/libssh,pouete/libssh,sebadoom/libssh,kedazo/libssh,DouglasHeriot/libssh,Distrotech/libssh,mwgoldsmith/ssh,robxu9/libssh,Distrotech/libssh,elastichosts/libssh,taikoo/libssh,nviennot/libssh,Distrotech/libssh,taikoo/libssh,DouglasHeriot/libssh,sebadoom/libssh,taikoo/libssh,bigcat26/libssh-mod,nviennot/libssh,pouete/libssh,bigcat26/libssh-mod,nviennot/libssh,sebadoom/libssh,DouglasHeriot/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh,kedazo/libssh,bigcat26/libssh-mod,mwgoldsmith/ssh,mwgoldsmith/ssh,robxu9/libssh,mwgoldsmith/ssh,wangshawn/libssh,mwgoldsmith/libssh,bigcat26/libssh-mod,wangshawn/libssh,sebadoom/libssh,DouglasHeriot/libssh,wangshawn/libssh,elastichosts/libssh,taikoo/libssh,kedazo/libssh,robxu9/libssh,nviennot/libssh,mwgoldsmith/libssh,wangshawn/libssh,Distrotech/libssh,elastichosts/libssh,kedazo/libssh