Add --trace-warnings flag

Author: sonicdoe

bin/_mocha

@@ -107,6 +107,7 @@ program
   .option('--throw-deprecation', 'throw an exception anytime a deprecated function is used')
   .option('--trace', 'trace function calls')
   .option('--trace-deprecation', 'show stack traces on deprecations')
+  .option('--trace-warnings', 'show stack traces on node process warnings')
   .option('--use_strict', 'enforce strict mode')
   .option('--watch-extensions <ext>,...', 'additional extensions to monitor with --watch', list, [])
   .option('--delay', 'wait for async suite definition')

bin/mocha

@@ -44,6 +44,7 @@ process.argv.slice(2).forEach(function (arg) {
     case '--log-timer-events':
     case '--throw-deprecation':
     case '--trace-deprecation':
+    case '--trace-warnings':
     case '--use_strict':
     case '--allow-natives-syntax':
     case '--perf-basic-prof':