modified_cof_cb() issues a updateAppearanceFromCOF() right before this function - removed extra update call. Sh-3650 & Sh-3985

Local bakes were following folder links in some cases, causing unworn items to be rendered.
Fixed the cof fetcher, now they should no longer show up.

Fixed potential memory leak in LLHTTPClient.  Fixed potential hanging http requests in LLHTTPClient.  Fixed munging of "Pragma" headers in LLHTTPClientAdapter

re-introduced don's refactor of low-level openGL calls pulling out of llui
and putting them into llrender. Took the new code from their updated versions
from the CHUI merge, but put them in a place accessible to appearance utility.

We were using an indicator of whether there *was* a baked texture to whether we
were *using* a baked texture. Switched to one of the (several) proper indicators
of whether a baked texture was in use. This should allow local texture data to
get marked for download when we enter appearance mode.

Local testing confirms that old apperances linger for a second or two, but are
soon replaced by the correct local renders.

SH-3959 WIP - pass information about type of fetched image - server bake, host bake, map tile, etc - down the chain so LLTextureFetchWorker can adjust behavior as needed

We suppress texture downloads for local textures not needed with server side
baking. We need to explicitly re-set texture priority for local textures
when entering appearance mode.

Fixing issues with not detecting when LLSD XML parsing fails.  Changing most http error handlers to understand LLSD error responses.  Fleshing out most http error handler message spam.

CHUI-772 FIX User sees no notification of conversation activity not visible in long scrolling conversation list
Added call to setSelectedSession() from LLConversationViewParticipant::handleMouseDown()