gfio: graphing updates

- Don't draw tickmark labels for an empty graph
- Remove Y-axis label. It was a bit awkward and hard to read.
- Ensure that we always put proper units on the Y-axis graph.
- Ensure that we always include the top most Y-axis tickmark
  and make that the ceiling, not the highest Y value. It's hard
  to visually understand a graph that is drawing somewhere above
  the last labeled tickmark.
- Fix rounding errors in graph.c

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/tickmarks.h b/tickmarks.h
index a8c1bf9..1e310db 100644
--- a/tickmarks.h
+++ b/tickmarks.h
@@ -7,6 +7,6 @@
 };
 
 int calc_tickmarks(double min, double max, int nticks, struct tickmark **tm,
-			int *power_of_ten, int use_KMG_symbols);
+			int *power_of_ten, int use_KMG_symbols, int base_off);
 
 #endif