got rid of "string s" by initializing it

and used [ v, "s" ], [ v, "m" ] in the following methods for Singular:
. GetListListOfHomalgMatrixAsString
. SaveHomalgMatrixToFile
. LoadHomalgMatrixFromFile
(it sometimes caused errors when using s as a ring indeterminate;
 this started occuring as I began to use the parametric
 Weyl algebra D[s] for the collaboration with Paco)