merge changes for 5.1.6-release

.hgtags

autobuild.xml

doc/contributions.txt

indra/llappearance/llwearable.cpp

indra/llcommon/llfile.cpp

indra/llcommon/llfile.h

indra/llcommon/tests/llsdserialize_test.cpp

indra/llmessage/llinstantmessage.cpp

indra/llmessage/llinstantmessage.h

indra/llmessage/llxfer.cpp

indra/llmessage/llxfer.h

indra/llmessage/llxfer_file.cpp

indra/llmessage/llxfer_file.h

indra/llmessage/llxfer_mem.cpp

indra/llmessage/llxfer_mem.h

indra/llmessage/llxfer_vfile.cpp

indra/llmessage/llxfer_vfile.h

indra/llmessage/llxfermanager.cpp

indra/llmessage/llxfermanager.h

indra/llplugin/llpluginclassmedia.h