Merge branch 'lindenlab/release' (6.4.20) into viewer/build

doc/contributions.txt

indra/llinventory/llparcel.h

indra/llinventory/llparcelflags.h

indra/llui/CMakeLists.txt

indra/llui/llbutton.cpp

indra/llui/llchat.h

indra/llui/llfloater.cpp

indra/llui/llfloater.h

indra/llui/llfloaterreg.cpp

indra/llui/llfloaterreg.h

indra/llui/lllineeditor.h

indra/llui/llmenugl.cpp

indra/llui/llnotifications.cpp

indra/llui/llnotifications.h

indra/llui/llsearcheditor.cpp

indra/llui/llsearcheditor.h

indra/llui/lltabcontainer.cpp

indra/llui/lltoolbar.cpp

indra/llui/lluictrl.cpp

indra/llui/lluictrl.h