build: make 'npm install' work reliably and issue build warning when node_modules look stale

This is done a in bit kludgy way on purpose so that it works on Windows and CI.

Works around npm/npm#8452.

Closes #2038

tools/check-environment.js

@@ -0,0 +1,39 @@
+var exec = require('child_process').exec;
+var semver = require('semver');
+
+var checkNodeModules = require('./npm/check-node-modules.js');
+
+
+function checkEnvironment(reqs) {
+
+  exec('npm --version', function(e, stdout) {
+    var foundNpmVersion = semver.clean(stdout);
+    var foundNodeVersion = process.version;
+    var issues = [];
+
+
+    if (!semver.satisfies(foundNodeVersion, reqs.requiredNodeVersion)) {
+      issues.push('You are running unsupported node version. Found: ' + foundNodeVersion +
+        ' Expected: ' + reqs.requiredNodeVersion + '. Use nvm to update your node version.');
+    }
+
+    if (!semver.satisfies(foundNpmVersion, reqs.requiredNpmVersion)) {
+      issues.push('You are running unsupported npm version. Found: ' + foundNpmVersion +
+        ' Expected: ' + reqs.requiredNpmVersion + '. Run: npm update -g npm');
+    }
+
+    if (!checkNodeModules()) {
+      issues.push('Your node_modules directory is stale or out of sync with npm-shrinkwrap.json. Run: npm install');
+    }
+
+    if (issues.length) {
+      console.warn(Array(80).join('!'));
+      console.warn('Your environment is not in a good shape. Following issues were found:');
+      issues.forEach(function(issue) {console.warn('  - ' + issue)});
+      console.warn(Array(80).join('!'));
+    }
+  });
+}
+
+
+module.exports = checkEnvironment;