Provide caching in homebox_build to improve page load time.

Issue Summary

In the homebox_build function there is a call to
$info[$block['module']] = module_invoke($block['module'], 'block', 'list');

If this page is being called frequently there is a significant overhead in collecting this information.
Especially if you have a lot of views.

If we cache this $info array it improves the performance.