From Philippe Pillot.

From Philippe Pillot.

Move part of the MUON display into the official macros based on
visscan_init.C.

Divided the parameter to visscan macros "show_extra_geo" into 2
parameters "show_muon" (kTRUE by default) and "show_trd" (kFALSE by
default as before).

In addition to the MUON geometry, I plot the MUON tracks and clusters
and add the other macros to the list without drawing.

Check if AliEn is initialized via GSHELL_ROOT environment variable
instead of alien_API_VO which is not always defined.