Remaining work:
1) Clone content_html_data
2) Cloning content_css_data requires the charset of the old content
3) Calling hlcache_handle_abort() before a content has been created must clean up the retrieval context.
svn path=/trunk/netsurf/; revision=10236
It is now defined as converting the content into a state in which it is ready for use.
The user of the content is now responsible for performing an initial reformat (sic) of the content before it can be redrawn.
Purge width/height parameters from hlcache_handle_retrieve/content_convert/*_convert APIs.
Fix up content handlers affected by the above change in semantics.
Ensure that browser_window_callback performs an initial reformat of its content.
svn path=/trunk/netsurf/; revision=10207
