Add original unix v6

source/iolib/unget.c

@@ -0,0 +1,15 @@
+# include "ciodec.c"
+ungetc (c, fn)
+{
+struct fileps *fp;
+if (nargs() != 2)
+   IEHzap("ungetc");
+/* push back onto input */
+fp = &IEH3fpts[fn];
+if (fp->wrflag == 0)
+	IEH3mbuf(fn,0);
+if (fp->bptr <= fp->buff - 100)
+	IEH3err("ungetc/unprintf: buffer full file %d",fn);
+*--fp->bptr = c;
+fp->nchars++;
+}