Header container moves from a vector of raw lines to a vector
of string pairs representing name/value pairs in headers.  For
incoming headers, we normalize the name to lowercase and trim
it.  Values are only left-trimmed.  Outgoing headers are left
as-is.  Simple find() method for the common case, forward and
reverse iterators for those few who need to do it themselves.
The HTTP status line (e.g. 'HTTP/1.1 200 Ok') is no longer treated
as a header to be returned to caller.  Unit tests, as usual,
were a bear but they absolutely ensured outgoing HTTP header
conformance after the change.  Grunt work paid off.

LLTextureFetch was also given a second options structure
for texture fetches.  Same as the original but with header return
to caller requested.  Baked textures should use this, the other
20,000 texture fetch requests should continue to use the original.

Renaming HTTP_HEADER_* into HTTP_IN_HEADER_* and HTTP_OUT_HEADER_* to make it more clear which header strings should be used for incoming vs outgoing situations.
Using constants for commonly used llhttpnode context strings.

Added an additional sanity check to make sure that other avatars don't
affect your wearables.

Reverting fix as additional problems were found that could lead to even accidental nudity.
This fix is not required for the current release as it is not a regression.
Will review options for fixing for the next release.

Added a constraint to ensure that the avatar's height (with offset)
does not go below 0.1 meters. Camera was getting confused since the avatar's
effective height was negative.

Note the avatar is mostly underground/contorted even at 0.1 meters, but
most users setting values this low will be making ultra-tinies and would
be hiding the avatar mesh. Camera stays above ground when height is at 0.1.

SH-4057 FIX - host bake textures should start with UDP fetching now, instead of waiting to fail down

Renamed logCapabilites static function to log_capabilities in llviewerregion.cpp to better match coding standard.

Updated logic for teen accounts, to ensure that during any transition
that they are wearing at least one undershirt wearable and one
underpants wearable.

Added the height offset in one too many places. fixing.

If we get more caps from a subsequent grant for a region, go ahead and use them. This is a hack that should be safe to remove after SH-3895 is fixed everywhere on the sim side.

CHUI-896 : ADD FIX : Line flashing and FUI button flashing not working correctly for CHUI notifications
backed out 902caf2 and (partly) d498514; case "NOT_ON_TOP" was fixed

CHUI-796 (User doesn't get all messages in 'do not disturb' mode): Now when a conversation is focused by clicking on it's line item, selecting a torn off floater or unminimized a torn off floater the stored notifications for that conversation will be removed.