visibility macros and flush() added to SrcFileSource; merge with master

diff --cc gtk2_ardour/sfdb_ui.cc
Simple merge

diff --cc libs/ardour/ardour/panner_shell.h
Simple merge

diff --cc libs/ardour/ardour/route.h
Simple merge

diff --cc libs/ardour/route.cc
Simple merge

diff --cc libs/ardour/wscript
Simple merge