browser-tests - disable timeouts for Mocha 1.21 … 

Commit 17a3ca7 set timeout to Infinity, but this still doesn't solve the issue reported in #961 if you use Mocha 1.21 (remove `node_modules` and do `npm install` to see that the current state of art is not sufficient)

This commit changes the config for grunt test run to `enableTimeouts=false`, and documents the equivalent command line switch (`--no-timeouts`) for mocha executable.