Merge from origin/emacs-25

eaa00584ceb Improve documentation of 'gnutls-verify-error'
908498cc01b ; etc/PROBLEMS: Describe GTK-related crashes on elementar...
741daec617e ; Describe the problem with ksh when resizing shell window

diff --cc etc/PROBLEMS
Simple merge

diff --cc lisp/net/gnutls.el
Simple merge