Make src headers idempotent and standalone

Redo src/*.h so that each include file is idempotent (that is, can
be included multiple times with the latter inclusions having no
effect) and standalone (that is, can be included by itself,
with no include file other than config.h needed as a prerequisite).
This is standard practice in GNU programs nowadays.
* lwlib/lwlib-widget.h, src/buffer.h, src/category.h, src/character.h:
* src/charset.h, src/coding.h, src/commands.h, src/disptab.h:
* src/fontset.h, src/gnutls.h, src/indent.h, src/keymap.h, src/macros.h:
* src/regex.h [emacs]:
* src/syntax.h, src/systty.h, src/termhooks.h:
Include lisp.h, for Lisp_Object.
* src/buffer.h, src/category.h, src/cm.h, src/commands.h, src/disptab.h:
* src/indent.h, src/intervals.h, src/keyboard.h, src/macros.h:
* src/process.h, src/puresize.h, src/region-cache.h, src/syntax.h:
* src/syssignal.h, src/sysstdio.h, src/systty.h, src/termchar.h:
* src/termopts.h, src/tparam.h, src/unexec.h:
Protect against multiple inclusion.
* src/buffer.h: Include character.h, for STRING_CHAR.
* src/emacsgtkfixed.h (struct frame):
* src/fontset.h (struct face):
* src/region-cache.h (struct buffer):
* src/termhooks.h (struct glyph):
* src/xsettings.h (struct x_display_info):
Add possibly-forward decl.
* src/syntax.h: Include buffer.h, for BVAR.
* src/sysselect.h: Include lisp.h, for eassume.
* src/termchar.h: Include <stdio.h>, for FILE.
* src/widget.h: Include <X11/IntrinsicP.h>, for Widget.
* src/xsettings.h: Include <X11/Xlib.h>, for XEvent.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/commands.h b/src/commands.h
index 19cd2e49890..e9383341cc9 100644
--- a/src/commands.h
+++ b/src/commands.h
@@ -16,6 +16,10 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_COMMANDS_H
+#define EMACS_COMMANDS_H
+
+#include "lisp.h"
 
 #define Ctl(c) ((c)&037)
 
@@ -39,3 +43,5 @@ extern Lisp_Object unread_switch_frame;
 /* Nonzero if input is coming from the keyboard.  */
 
 #define INTERACTIVE (NILP (Vexecuting_kbd_macro) && !noninteractive)
+
+#endif /* EMACS_COMMANDS_H */