merge changes for 5.1.4-release

.hgtags

doc/contributions.txt

indra/llappearance/lltexlayer.cpp

indra/llcommon/llmemory.cpp

indra/llcommon/llmemory.h

indra/llcommon/llsdserialize.cpp

indra/llcommon/llsdserialize.h

indra/llcommon/llsdserialize_xml.cpp

indra/llcommon/llthread.cpp

indra/llimage/llimage.cpp

indra/llimage/llimage.h

indra/llimage/llimagedxt.cpp

indra/llimage/llimagej2c.cpp

indra/llmath/llvolume.cpp

indra/llmath/llvolume.h

indra/llmessage/llavatarnamecache.cpp

indra/llplugin/llpluginclassmedia.cpp

indra/llrender/llfontfreetype.cpp

indra/llrender/llfontfreetype.h

indra/llrender/llfontregistry.cpp