Fix analogWrite to list only PWM pins and warn if input is out of range.

Fixes #30

blockly/blocks/arduino/io.js

@@ -124,7 +124,7 @@ Blockly.Blocks['io_analogwrite'] = {
     this.appendDummyInput('')
         .appendField('set analogue pin#')
         .appendField(new Blockly.FieldDropdown(
-            Blockly.Arduino.Boards.selected.analogPins), 'PIN');
+            Blockly.Arduino.Boards.selected.pwmPins), 'PIN');
     this.appendValueInput('NUM', Blockly.StaticTyping.BlocklyType.NUMBER)
         .appendField('to')
         .setCheck(Blockly.StaticTyping.BlocklyType.NUMBER);
@@ -138,7 +138,7 @@ Blockly.Blocks['io_analogwrite'] = {
    * @this Blockly.Block
    */
   updateFields: function() {
-    Blockly.Arduino.Boards.refreshBlockFieldDropdown(this, 'PIN', 'analogPins');
+    Blockly.Arduino.Boards.refreshBlockFieldDropdown(this, 'PIN', 'pwmPins');
   },
   /** @return {!string} The type of input value for the block, an integer. */
   getBlockType: function() {

blockly/generators/arduino/io.js

@@ -94,6 +94,14 @@ Blockly.Arduino['io_analogwrite'] = function(block) {
   var pinSetupCode = 'pinMode(' + pin + ', OUTPUT);';
   Blockly.Arduino.addSetup('io_' + pin, pinSetupCode, false);
 
+  // Warn if the input value is out of range
+  if ( (stateOutput < 0) || (stateOutput > 255)) {
+    block.setWarningText('The analgue value must be between 0 and 255',
+                         'pwm_value');
+  } else {
+    block.setWarningText(null, 'pwm_value');
+  }
+
   var code = 'analogWrite(' + pin + ',' + stateOutput + ');\n';
   return code;
 };