Be more tolerant to fonts named "Foobar-12"

Be more tolerant to fonts named "Foobar-12"

* src/frame.c (x_set_font): If font_spec_from_name returns nil,
don't barf; instead, request a new fontset to be generated.  This
avoids unnecessarily rejecting fonts named against XLFD rules.  See
http://lists.gnu.org/archive/html/help-emacs-windows/2015-06/msg00001.html,
for the description of the original problem.

* lisp/faces.el (set-face-attribute): Don't be fooled too easily
by a hyphen in a font's name.