Don't abort try_window with fonts change when showing tooltip (Bug#2423).

Don't abort try_window with fonts change when showing tooltip (Bug#2423).

* dispextern.h (TRY_WINDOW_CHECK_MARGINS)
(TRY_WINDOW_IGNORE_FONTS_CHANGE): New defines.

* xdisp.c (try_window): Change arg from CHECK_MARGINS to FLAGS.
Don't abort with fonts change if TRY_WINDOW_IGNORE_FONTS_CHANGE is
set in FLAGS.  Callers with non-zero CHECK_MARGINS changed to use
TRY_WINDOW_CHECK_MARGINS.

* xfns.c (Fx_show_tip): Call try_window with TRY_WINDOW_IGNORE_FONTS_CHANGE.