control/bug getodk#157: fix two minor issues with numeric range.

* default values were floats rather than strings. when one edits the
  textbox it drops strings in, so we should emulate that.
* zero and negative values should not be permitted for step.

public/javascripts/control.js

@@ -549,7 +549,7 @@
                         inclusivity: false,
                         description: 'The lowest and highest selectable values, inclusive.',
                         tips: [ 'Integers and decimals are both valid.' ],
-                        value: { min: 1, max: 10 },
+                        value: { min: "1", max: "10" },
                         summary: false },
           selectStep: { name: 'Selectable Range: Step Between Choices',
                         type: 'text',

public/javascripts/impl.validation.js

@@ -172,7 +172,10 @@
             check: function(step, range)
             {
                 // can't use % because js float nastiness.
-                var quotient = (parseFloat(range.max) - parseFloat(range.min)) / parseFloat(step);
+                var step = parseFloat(step);
+                if (step <= 0) return false;
+
+                var quotient = (parseFloat(range.max) - parseFloat(range.min)) / step;
                 return Math.floor(quotient) === quotient;
             },
             message: 'Step must divide the selectable range perfectly into evenly-sized increments.',