Versions of MGR files.

PILAR keeps a copy of the N last versions of MGR files. Namely

name.mgr            last (current) version

name_1.mgr        previous version

name_2.mgr        second previous version

…   …   …

name_N.mgr        Nth previous version (oldest version retained)

When xxx.mgr file is saved, for roll versions set to 3, the following sequence is followed:

drop ß xxx_3.mgr ß xxx_2.mgr ß xxx_1.mgr ß xxx.mgr