Make minSize customizable

Previously, the minimum size a selection could be was set at five
pixels. This commit adds the ability to customize this value.

jquery.flot.selection.js

@@ -9,7 +9,7 @@ selection: {
 	mode: null or "x" or "y" or "xy",
 	color: color,
 	shape: "round" or "miter" or "bevel",
-	alwaysShow: boolean
+	minSize: number of pixels
 }
 
 Selection support is enabled by setting the mode to one of "x", "y" or "xy".
@@ -17,9 +17,17 @@ In "x" mode, the user will only be able to specify the x range, similarly for
 "y" mode. For "xy", the selection becomes a rectangle where both ranges can be
 specified. "color" is color of the selection (if you need to change the color
 later on, you can get to it with plot.getOptions().selection.color). "shape"
-is the shape of the corners of the selection. When "alwaysShow" is true,
-the selection rectangle will always be displayed (as a line), even when the
-selection is very small.
+is the shape of the corners of the selection.
+
+"minSize" is the minimum size a selection can be in pixels. This value can
+be customized to determine the smallest size a selection can be and still
+have the selection rectangle be displayed. When customizing this value, the
+fact that it refers to pixels, not axis units must be taken into account.
+Thus, for example, if there is a bar graph in time mode with BarWidth set to 1
+minute, setting "minSize" to 1 will not make the minimum selection size 1
+minute, but rather 1 pixel. Note also that setting "minSize" to 0 will prevent
+"plotunselected" events from being fired when the user clicks the mouse without
+dragging.
 
 When selection support is enabled, a "plotselected" event will be emitted on
 the DOM element you passed into the plot function. The event handler gets a
@@ -37,7 +45,8 @@ parameters as the "plotselected" event, in case you want to know what's
 happening while it's happening,
 
 A "plotunselected" event with no arguments is emitted when the user clicks the
-mouse to remove the selection.
+mouse to remove the selection. As stated above, setting "minSize" to 0 will
+destroy this behavior.
 
 The plugin allso adds the following methods to the plot object:
 
@@ -279,7 +288,7 @@ The plugin allso adds the following methods to the plot object:
         }
 
         function selectionIsSane() {
-            var minSize = 5;
+            var minSize = plot.getOptions().selection.minSize;
             return Math.abs(selection.second.x - selection.first.x) >= minSize &&
                 Math.abs(selection.second.y - selection.first.y) >= minSize;
         }
@@ -299,9 +308,9 @@ The plugin allso adds the following methods to the plot object:
 
         plot.hooks.drawOverlay.push(function (plot, ctx) {
             // draw selection
-            var o = plot.getOptions();
-            if (selection.show && (selectionIsSane() || o.selection.alwaysShow)) {
+            if (selection.show && selectionIsSane()) {
                 var plotOffset = plot.getPlotOffset();
+                var o = plot.getOptions();
 
                 ctx.save();
                 ctx.translate(plotOffset.left, plotOffset.top);
@@ -342,7 +351,7 @@ The plugin allso adds the following methods to the plot object:
                 mode: null, // one of null, "x", "y" or "xy"
                 color: "#e8cfac",
                 shape: "round", // one of "round", "miter", or "bevel"
-                alwaysShow: false // boolean
+                minSize: 5 // minimum number of pixels
             }
         },
         name: 'selection',