standard input not a tty

When hugs's standard input is not a tty, this patch stops it prompting
or attempting to use readline.  It also disables $$ in that situation;
this could be changed if desired, but is probably the right thing.

If it is put it in, the --with-readline option of configure can probably
be ditched (i.e. set USE_READLINE if editline or readline is available).

Index: src/input.c
===================================================================
RCS file: /home/cvs/root/hugs98/src/input.c,v
retrieving revision 1.43
diff -u -r1.43 input.c
--- src/input.c	2002/06/14 14:41:10	1.43
+++ src/input.c	2002/07/18 15:58:05
@@ -264,6 +264,7 @@
 #define SCRIPTFILE 2                   /* - script file                    */
 #define PROJFILE   3                   /* - project file                   */
 #define STRING     4                   /* - string buffer?                 */
+#define NOKEYBOARD 5                   /* - standard input, but not a tty  */
 
 static Int    reading   = NOTHING;
 
@@ -322,6 +323,12 @@
     hereState   = START;
 #endif
 
+#ifdef HAVE_ISATTY
+    if (!isatty(fileno(stdin))) {	/* not reading from a tty:         */
+	reading = NOKEYBOARD;		/* don't prompt or try readline    */
+	return;
+    }
+#endif
 #if USE_READLINE
     /* Paranoid freeing code supplied by Sverker Nilsson ([email protected]) 
      * avoids accidentally freeing currentLine twice. 
@@ -607,6 +614,9 @@
 		    c1 = ' ';
 		}
 	    }
+	} 
+	else if (reading==NOKEYBOARD) {
+	    c1 = c0=='\n' ? EOF : getc(stdin);
 	} 
 	else if (reading==STRING) {
 	    c1 = (unsigned char) *nextStringChar++;