Add babelcheck.js

As per 4bea0c0818

babelcheck.js

@@ -0,0 +1,23 @@
+var exec = require('child_process').exec;
+
+// Makes sure the babel executable in the path is babel 6 (or greater), not
+// babel 5, which it is if you upgrade from an older version of react-sdk and
+// run 'npm install' since the package has changed to babel-cli, so 'babel'
+// remains installed and the executable in node_modules/.bin remains as babel
+// 5.
+
+// This script is duplicated from matrix-react-sdk because it can't reliably
+// be pulled in from react-sdk while npm install is failing, as it will do
+// if the environment is in the erroneous state this script checks for.
+
+exec("babel -V", function (error, stdout, stderr) {
+    if ((error && error.code) || parseInt(stdout.substr(0,1), 10) < 6) {
+        console.log("\033[31m\033[1m"+
+            '*****************************************\n'+
+            '* vector-web has moved to babel 6       *\n'+
+            '* Please "rm -rf node_modules && npm i" *\n'+
+            '*****************************************\n'+
+        "\033[91m");
+        process.exit(1);
+    }
+});

package.json

@@ -19,7 +19,7 @@
     "build:bundle": "NODE_ENV=production webpack -p lib/vector/index.js vector/bundle.js",
     "build:bundle:dev": "webpack --optimize-occurence-order lib/vector/index.js vector/bundle.js",
     "build:staticfiles": "cpx -v node_modules/olm/olm.js vector/",
-    "build": "npm run build:staticfiles && npm run build:emojione && npm run build:css && npm run build:compile && npm run build:bundle",
+    "build": "node babelcheck.js && npm run build:staticfiles && npm run build:emojione && npm run build:css && npm run build:compile && npm run build:bundle",
     "build:dev": "npm run build:staticfiles && npm run build:emojione && npm run build:css && npm run build:compile && npm run build:bundle:dev",
     "package": "scripts/package.sh",
     "start:emojione": "cpx \"node_modules/emojione/assets/svg/*\" vector/emojione/svg/ -w",
@@ -28,7 +28,7 @@
     "start:skins:css": "catw \"src/skins/vector/css/**/*.css\" -o vector/components.css",
     "start:staticfiles": "cpx -Lwv node_modules/olm/olm.js vector/",
     "//cache": "Note the -c 1 below due to https://code.google.com/p/chromium/issues/detail?id=508270",
-    "start": "parallelshell \"npm run start:staticfiles\" \"npm run start:emojione\" \"npm run start:js\" \"npm run start:skins:css\" \"http-server -c 1 vector\"",
+    "start": "node babelcheck.js && parallelshell \"npm run start:staticfiles\" \"npm run start:emojione\" \"npm run start:js\" \"npm run start:skins:css\" \"http-server -c 1 vector\"",
     "start:prod": "parallelshell \"npm run start:staticfiles\" \"npm run start:emojione\" \"npm run start:js:prod\" \"npm run start:skins:css\" \"http-server -c 1 vector\"",
     "clean": "rimraf lib vector/olm.js vector/bundle.css vector/bundle.js vector/bundle.js.map vector/webpack.css* vector/emojione",
     "prepublish": "npm run build:css && npm run build:compile",