More PGTK related cleanup

More PGTK related cleanup

* src/pgtkfns.c (x_set_foreground_color, x_set_background_color)
(x_set_border_color, x_set_cursor_color, x_set_title)
(x_set_menu_bar_lines, x_set_tab_bar_lines, x_set_tool_bar_lines)
(x_set_child_frame_border_width, x_set_internal_border_width)
(x_set_icon_type, x_set_icon_name, x_set_cursor_type)
(x_set_mouse_color, x_set_undecorated, x_set_skip_taskbar)
(x_set_override_redirect, pgtk_frame_parm_handlers)
(Fx_create_frame): Rename most `x_' functions to `pgtk_' ones.
All callers changed.
* src/pgtkmenu.c (Fx_menu_bar_open_internal): Remove duplicate
doc string definition.
* src/pgtkterm.c (x_set_offset, pgtk_iconify_frame)
(x_set_parent_frame, x_set_no_focus_on_map, x_set_no_accept_focus)
(x_set_z_group, x_set_cursor_gc, x_set_mouse_face_gc)
(x_set_mode_line_face_gc, x_set_glyph_string_gc)
(x_set_glyph_string_clipping, x_set_glyph_string_clipping_exactly)
(x_setup_relief_color, x_setup_relief_colors)
(x_set_clip_rectangles, x_draw_relief_rect, x_draw_box_rect)
(x_draw_glyph_string_box, x_draw_image_relief)
(x_draw_image_foreground, x_draw_stretch_glyph_string)
(pgtk_draw_glyph_string, x_set_toolkit_scroll_bar_thumb)
(x_set_toolkit_horizontal_scroll_bar_thumb)
(pgtk_set_vertical_scroll_bar, pgtk_set_horizontal_scroll_bar)
(x_set_frame_alpha, frame_highlight, frame_unhighlight)
(pgtk_create_terminal, map_event): Rename most `x_' functions to
`pgtk_' ones.  All callers changed.
* src/pgtkterm.h: Update prototypes.