Change how the backend emulator library is initialized for libSIDPlay2 and FP, as it seems the engine configuration has some persistence despite reconfiguration between loaded files if same engine object is retained. This caused, for example, 2SID stereo tunes being played "mono" if played after a normal 1-SID tune. Duh.

src/xmms-sid.c
src/xmms-sid.h
src/xs_config.c
src/xs_fileinfo.c
src/xs_glade.c
src/xs_glade.h
src/xs_interface.c
src/xs_length.c
src/xs_stil.c
src/xs_sidplay1.cpp
src/xs_sidplay2.cpp
src/xs_sidplayfp.cpp
src/xs_about.c