gdkx.h should have c-linkage specifier

[TANAKA Shinya <tanaka garlic q t u-tokyo ac jp>]

very small fix.
gdkx.h should have `__cplusplus' check.

------------------------------------------------------------
tanaka@garlic.q.t.u-tokyo.ac.jp



*** gdkx.h.org  Wed Jan 27 13:28:15 1999
--- gdkx.h      Wed Jan 27 13:30:36 1999
***************
*** 37,42 ****
--- 37,45 ----
  #define GDK_FONT_XDISPLAY(font)       (((GdkFontPrivate*) font)->xdisplay)
  #define GDK_FONT_XFONT(font)          (((GdkFontPrivate*) font)->xfont)
  
+ #ifdef __cplusplus
+ extern "C" {
+ #endif /* __cplusplus */
  
  GdkVisual*   gdkx_visual_get   (VisualID xvisualid);
  /* XXX: Do not use this function until it is fixed. An X Colormap
***************
*** 50,54 ****
--- 53,61 ----
  /* Functions to create pixmaps and windows from their X equivalents */
  GdkPixmap    *gdk_pixmap_foreign_new (guint32     anid);
  GdkWindow    *gdk_window_foreign_new (guint32      anid);
+ 
+ #ifdef __cplusplus
+ }
+ #endif /* __cplusplus */
  
  #endif /* __GDK_X_H__ */