Fix issues related to pixelwise resizing. (Bug#16013) (Bug#16033)

Fix issues related to pixelwise resizing.  (Bug#16013) (Bug#16033)

* window.c (Fset_window_new_pixel): Don't choke at negative
argument value (Bug#16033).

* xfns.c (Fx_create_frame): Add another call to change_frame_size
to avoid crash in window_box_height.

* gtkutil.h: Fix external declaration of xg_frame_set_char_size.
* gtkutil.c (xg_frame_set_char_size, style_changed_cb): Fix size
calculation.
* xterm.c (x_set_window_size): Fix size calculation (Bug#16013).