Convert LLCore::HttpHeaders to use shared_ptr<> rather than an intrusive_ptr<> for refrence counting.

Added get/setRequestURL() to LLCore::HttpResponse
Removed URI from the HttpSDHandler.

Added second mesh class as well as an asset upload class.
Refactored initialization to use less code and more data to
cleanly get http started.  Modified mesh to use the new
http class for large requests (>2MB for now).  Added additional
timeout setting to llcorehttp to distinguish connection timeout
from transport timeout and are now using transport timeout
values for large asset downloads that may need more time.

When a Content-Range header is received, make available the full triplet of <offset, length, fulllength>.

This is the first functional viewer pass with the HTTP work of the texture fetch
code performed by the llcorehttp library.  Not exactly a 'drop-in' replacement
but a work-alike with some changes (e.g. handler notification in consumer
thread versus responder notification in worker thread).

This also includes some temporary changes in the priority scheme to prevent
the kind of priority inversion found in VWR-28996.  Scheme used here does
provide liveness if not optimal responsiveness or order-of-operation.

The llcorehttp library at this point is far from optimally performing.
Its worker thread is making relatively poor use of cycles it gets and
it doesn't idle or sleep intelligently yet.  This early integration step
helps shake out the interfaces, implementation niceties will be covered
soon.

The unit/integration tests don't work yet as I'm still battling cmake/autobuild
as usual but first milestone passed.

object inventory offers don't increment system menu count
added customizable merging behavior for duplicate "unique" notifications
fixed overeager notification channels

phase 1, removal of most of llnotificationhandler

Result of svn merge -r107256:107258 svn+ssh://svn/svn/user/phoenix/license_2009_merge into trunk. QAR-1165

Result of svn merge -r71162:71205 svn+ssh://svn/svn/linden/branches/new-license into release. only changes files which are not deployed or the comments section of code.