ENHANCE: In PcSeries do not induce if the pcgs is being built

There are two different situations in which PcSeries is called. The first is
a good pcgs and we happen to want the series -- this is the existing code.

The second case is that the series is needed to do anything with the pcgs.
In this case inducing caused bad recursions. Avoid this.

lib/pcgscomp.gi

@@ -192,20 +192,28 @@ end );
 ##
 InstallMethod( PcSeries,"construct subgroups", true, [ IsPcgs ], 0,
 function( pcgs )
-    local   grp,  series,  i;
+local   grp,  series,  i,hasro;
 
     # construct the group generated by <pcgs>
     #T  1996/10/01 fceller something seems to break for Difference or Set
     #T  grp := GroupByGenerators( pcgs, One(pcgs) );
 #T seems to work now, 1998/12/09 sam
 
     grp := GroupOfPcgs(pcgs);
+    hasro:=HasRelativeOrders(pcgs);
 
     # construct the series
     series := [ grp ];
     for i  in [ 2 .. Length(pcgs)+1 ]  do
+      if hasro then
+	# pcgs is all in place -- use induced pcgs for generators to build
+	# series after pcgs is at work
         Add( series, SubgroupByPcgs( grp,
 	  InducedPcgsByPcSequenceNC(pcgs,pcgs{[ i .. Length(pcgs) ]} ) ));
+      else
+        # pcgs is being built. Don't induce, but just use subgroup.
+        Add( series, SubgroupNC( grp, pcgs{[ i .. Length(pcgs) ]} ) );
+      fi;
     od;
 
     return series;