Cross-Project Tracking: function_exists() Checks

[justintadlock]

Because we intend to allow HC and its sub-projects to be bundled with multiple projects (see: #183), we need to account for the repos with functions (not just classes). The easiest way to do this is to wrap each function with a function_exists() check like so:

if ( ! function_exists( __NAMESPACE__ . '\\func_name' ) ) {
// Function
}

Long term, we might consider phasing out functions with a static helper class instead. That way, the class autoloader bypasses the issue (file autoloading doesn't).