fix for crash on exit resulting from 8c0e024d0c33

various fixes to lltrace
start() on started recording no longer resets
fixed various instances of unit forgetfullness in lltrace
recording split now has gapless timing
scene monitor now guarantees min sample time
renamed a bunch of stats
added names to debug thread view on windows

also, removed LLTrace::init and cleanup
removed derived class implementation of memory stat for LLMemTrackable
is automatic now

removed LLThreadLocalSingleton
collapsed all thread recorder classes to single type, LLTrace::ThreadRecorder
moved fasttimer stack head to llthreadlocalsingletonpointer via ThreadRecorder

fixed some lltrace logic errors
more consistent syncing of timestamps of sample values in recording stack
selection of primary buffers was completely incorrect
assignment of recordings got wrong play state due to implicit
operator = defined in base class
fixed asset stats only working up to the first send

pulled swap() out of ui time block
cleaned up internal lltrace dependencies, factored out common accumulator definitions

reverted SlaveThreadRecorder update gating
moved processTimes() outside of Recording, so it is called only once per frame
refined sample merge logic so that multi-threaded samples do not stomp on linear history
of a stat

fixed LLTrace::ExtendablePeriodicRecording::extend() to include *all* frame extensions
gated SlaveThreadRecorder pushing to master based on master update rate
reverted changes to LLThreadLocalSingletonPointer to not use offset-from-default trick

fixed copy construction behavior of Recordings to not zero out data
split measurement into event and sample, with sample representing
a continuous function

removed extra dereference for copy on write pointer
moved copyonwrite mechanism to RecordingBuffers from individual buffer
fixed logic that was leaving scene unfrozen when camera moved during metrics gathering

fixed memory leak
fixed glitching of fast timer display

made fast timer stack thread local
added LLThreadLocalSingleton
made LLThreadLocalPointer obey pointer rules for const
added LLThreadLocalSingletonPointer for fast thread local pointers

improvements on lifetime of lltrace core data structures
tweaks to thread local pointer handling so that static constructors/destructors
can safely call functions that use lltrace

converted fast timer view over to new lltrace mechanisms

moved runtime timer tree topology information to separate array instead of recording stack

fixed trace data gathering and routing from background thread
simplified slave->master thread communication (eliminated redundant recording and proxy object)
improved performance of fast timer data gathering (slow iterators)

fixed trace recording on background threads hitting null pointer

cleaned up accumulator merging logic
introduced frame recording to LLTrace directly instead of going through LLViewerStats
moved consumer code over to frame recording instead of whatever the current active recording was

added update() method to trace recorders to allow mid-collection snapshots

moved threadrecorder classes into separate file
added Count trace type, which tracks value increases and decreases and can report churn
as well as overall growth rate