Improve file position handling on Big Engian machines

Added swap_HALFs(dest, src, len) function to byteswap.c.

Calc can now handle Big Engian file position sizes that are a
multiple of BASEB bits in length.  Before handle Big Engian file
positions could only be 32 and 64 bits in length.  This will allow,
for example, a Big Engian file position size of 128 (assuming that
128/BASEB is is an integer).

byteswap.c

@@ -40,7 +40,7 @@
  *	dest	- pointer to where the swapped src will be put or
  *		  NULL to allocate the storage
  *	src	- pointer to a HALF array to swap
- *	len	- length of the src HALF array
+ *	len	- length of the src HALF array in HALFs
  *
  * returns:
  *	pointer to where the swapped src has been put
@@ -276,7 +276,7 @@ swap_b8_in_COMPLEX(COMPLEX *dest, COMPLEX *src, BOOL all)
  *	dest	- pointer to where the swapped src will be put or
  *		  NULL to allocate the storage
  *	src	- pointer to a HALF array to swap
- *	len	- length of the src HALF array
+ *	len	- length of the src HALF array in HALFs
  *
  * returns:
  *	pointer to where the swapped src has been put
@@ -309,6 +309,50 @@ swap_b16_in_HALFs(HALF *dest, HALF *src, LEN len)
 }
 
 
+/*
+ * swap_HALFs - swap HALFs in an array of HALFs
+ *
+ * given:
+ *	dest	- pointer to where the swapped src will be put or
+ *		  NULL to allocate the storage
+ *	src	- pointer to a HALF array to swap
+ *	len	- length of the src HALF array in HALFs
+ *
+ * returns:
+ *	pointer to where the swapped src has been put
+ */
+HALF *
+swap_HALFs(HALF *dest, HALF *src, LEN len)
+{
+	HALF *s;	/* src swap pointer */
+	HALF *d;	/* dest swap pointer */
+	HALF *ret;
+	LEN i;
+
+	/*
+	 * allocate storage if needed
+	 */
+	if (dest == NULL) {
+		dest = alloc(len);
+	}
+	ret = dest;
+
+	/*
+	 * swap HALFs in the array
+	 */
+	s = src;
+	d = &dest[len-1];
+	for (i=0; i < len; ++i, --d, ++s) {
+		*d = *s;
+	}
+
+	/*
+	 * return the result
+	 */
+	return ret;
+}
+
+
 /*
  * swap_b16_in_ZVALUE - swap 16 bits in a ZVALUE
  *