Minor Description
The change for https://issues.apache.org/jira/browse/TS-185 makes sure that url_host_set() doesn't free/reallocate new memory on every call, but optimally grows the buffer. The old approach used to work as a copy-on-write mechanism when a URL object was cloned. A url_host_set() on either object decoupled the the host pointers from both objects pointing to the same location. The new approach however does not free/reallocate on every url_host_set() and there is a chance that upon cloning (which url_copy_onto() does) that both objects' host pointers will continue to point to the same location. To fix this, url_copy_onto() should duplicate the host string.
Also from TS-185, the addition of m_capacity_host has to be changed. The new member should be added towards the end of the class as this affects unmarshalling new classes from old cache files.