Improved logging of HTTP requests
- MemoryBuffer isn't seekable, so we can't log it. Log the string instead.
- Handle compressed streams
- Don't attempt to dump binary data. Either don't log it at all (if we know it's binary), or at least convert non-ASCII characters to ASCII.
- Log responses to HTTP requests
- Use the same log prefix for all of these log messages ("[LOGHTTP]"), to make them easy to see at a glance
- Increased the snippet length to 200 (80 doesn't show enough), and add "..." only if the message was actually truncated

Resolves http://opensimulator.org/mantis/view.php?id=6949
Always throw an exception if MakeRequest (used for HTTP POST) fails. (Previously many exceptions were ignored)

Resolves http://opensimulator.org/mantis/view.php?id=6949
In Core Profiles: as a fallback, try to get profiles from foreign grids using the OpenProfile protocol

Resolves http://opensimulator.org/mantis/view.php?id=6954