Distinguish between the first and innermost axis.

The fix for #1056 caused a regression where grid lines were drawn for
the innermost axes on both sides instead of just the first axis.
Fixed by properly distinguishing the first axis in each direction from
the innermost one on each side.  Fixes #1075.

jquery.flot.js

@@ -1400,37 +1400,50 @@ Licensed under the MIT license.
             var lw = axis.labelWidth,
                 lh = axis.labelHeight,
                 pos = axis.options.position,
+                isXAxis = axis.direction === "x",
                 tickLength = axis.options.tickLength,
                 axisMargin = options.grid.axisMargin,
                 padding = options.grid.labelMargin,
-                all = axis.direction == "x" ? xaxes : yaxes,
-                index, innermost;
-
-            // determine axis margin
-            var samePosition = $.grep(all, function (a) {
-                return a && a.options.position == pos && a.reserveSpace;
+                innermost = true,
+                outermost = true,
+                first = true,
+                found = false;
+
+            // Determine the axis's position in its direction and on its side
+
+            $.each(isXAxis ? xaxes : yaxes, function(i, a) {
+                if (a && a.reserveSpace) {
+                    if (a === axis) {
+                        found = true;
+                    } else if (a.options.position === pos) {
+                        if (found) {
+                            outermost = false;
+                        } else {
+                            innermost = false;
+                        }
+                    }
+                    if (!found) {
+                        first = false;
+                    }
+                }
             });
-            if ($.inArray(axis, samePosition) == samePosition.length - 1)
-                axisMargin = 0; // outermost
 
-            // Determine whether the axis is the first (innermost) on its side
+            // The outermost axis on each side has no margin
 
-            innermost = $.inArray(axis, samePosition) == 0;
+            if (outermost) {
+                axisMargin = 0;
+            }
 
-            // determine tick length - if we're innermost, we can use "full"
+            // The ticks for the first axis in each direction stretch across
 
             if (tickLength == null) {
-                if (innermost)
-                    tickLength = "full";
-                else
-                    tickLength = 5;
+                tickLength = first ? "full" : 5;
             }
 
             if (!isNaN(+tickLength))
                 padding += +tickLength;
 
-            // compute box
-            if (axis.direction == "x") {
+            if (isXAxis) {
                 lh += padding;
 
                 if (pos == "bottom") {