replace llinfos, lldebugs, etc with new LL_INFOS(), LL_DEBUGS(), etc.

moved object cache sampling code so that it actually gets executed
default values for stats are NaN instead of 0 in many cases

consolidated most indra-specific constants in llcommon under indra_constants.h
fixed issues with operations on mixed unit types (implicit and explicit)
made LL_INFOS() style macros variadic in order to subsume other logging methods
such as ll_infos
added optional tag output to error recorders

SH-4341: Interesting: Viewer crash in LLViewerOctreeCull

added commented out log timestamp override for scene load performance monitoring

there are no samples during the time period.
added hasValue to SampleAccumulator so we don't print a value when we don't have
a single sample yet
added some disabled log output for scene load timing

fixed normalization assertions to work with megaprims
added is_zero() utility function
fixed unit declarations to be more clear
fixed texture cache hit rate always being 0