Add support for analyzing test coverage with Istanbul

To use, make sure your Node installation is up to date and install
istanbul with npm:

  sudo npm install -g istanbul      # 'sudo' may be optional on OSX

Then run

  tools/test-js-with-node cover

and navigate to coverage/lcov-report/js/index.html in a browser.

(imported from commit 2da4894d1725e2f9540b3895304246e3cd138f6c)

.gitignore

@@ -16,3 +16,4 @@ zerver/fixtures/test_data1.json
 .kdev4
 humbug.kdev4
 memcached_prefix
+coverage/

tools/test-js-with-node

@@ -4,7 +4,13 @@ cd "$(dirname "$0")"/..
 
 export NODE_PATH=static
 
-# Run the index.js test runner, which runs all the other tests.
 INDEX_JS=zerver/tests/frontend/node/index.js
 NODEJS=$(which nodejs || which node)
-$NODEJS $INDEX_JS
+if [ f$1 = fcover ]; then
+  # Run a coverage test with Istanbul.
+  istanbul cover $INDEX_JS
+else
+  # Normal testing, no coverage analysis.
+  # Run the index.js test runner, which runs all the other tests.
+  $NODEJS $INDEX_JS
+fi