Merge branch 'ios-build' into devel

Allows to build projects with 'ios' platform included on linux machines that
cannot build for iOS. Creates an easier workaround for #2867.

tools/commands-cordova.js

@@ -79,6 +79,13 @@ cordova.buildTargets = function (localPath, targets, options) {
 
   verboseLog('Running build for platforms:', platforms);
   checkRequestedPlatforms(platforms);
+  platforms = _.filter(platforms, function (platform) {
+    if (! _.contains(availablePlatforms, platform)) {
+      Console.warn(platform + ': skipping platform not available on your system');
+      return false;
+    }
+    return true;
+  });
 
   _.each(platforms, function (platform) {
     requirePlatformReady(platform);

tools/commands.js

@@ -733,6 +733,8 @@ var buildCommand = function (options) {
                                appName: appName
                              }));
     } catch (err) {
+      if (err instanceof main.ExitWithCode)
+         throw err;
       Console.printError(err, "Error while building for mobile platforms");
       return 1;
     }
@@ -814,6 +816,7 @@ var buildCommand = function (options) {
     var platformPath = path.join(outputPath, platformName);
 
     if (platformName === 'ios') {
+      if (process.platform !== 'darwin') return;
       files.cp_r(buildPath, path.join(platformPath, 'project'));
       fs.writeFileSync(
         path.join(platformPath, 'README'),