sftp: Add references to sftp_get_error() to docs.
sftp: Add references to sftp_get_error() to docs.

DouglasHeriot/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh,robxu9/libssh,Distrotech/libssh,elastichosts/libssh,kedazo/libssh,Distrotech/libssh,pouete/libssh,bigcat26/libssh-mod,wangshawn/libssh,sebadoom/libssh,bigcat26/libssh-mod,taikoo/libssh,mwgoldsmith/libssh,bigcat26/libssh-mod,bigcat26/libssh-mod,nviennot/libssh,mwgoldsmith/ssh,DouglasHeriot/libssh,nviennot/libssh,taikoo/libssh,jt1/honeypot-libssh,mwgoldsmith/ssh,kedazo/libssh,nviennot/libssh,mwgoldsmith/ssh,jt1/honeypot-libssh,robxu9/libssh,wangshawn/libssh,jt1/honeypot-libssh,taikoo/libssh,wangshawn/libssh,kedazo/libssh,pouete/libssh,DouglasHeriot/libssh,sebadoom/libssh,robxu9/libssh,pouete/libssh,robxu9/libssh,pouete/libssh,taikoo/libssh,sebadoom/libssh,kedazo/libssh,elastichosts/libssh,nviennot/libssh,mwgoldsmith/ssh,DouglasHeriot/libssh,Distrotech/libssh,wangshawn/libssh,Distrotech/libssh,elastichosts/libssh,mwgoldsmith/libssh,jt1/honeypot-libssh,sebadoom/libssh