transformations: fix parsing of args of type termlist

examples/verifythis_fm2012_LRS/why3session.xml

@@ -352,13 +352,9 @@
   <goal name="VC lrs.20" expl="postcondition" proved="true">
   <transf name="introduce_premises" proved="true" >
    <goal name="VC lrs.20.0" expl="postcondition" proved="true">
-   <transf name="instantiate" proved="true" arg1="H7" arg2="x">
+   <transf name="instantiate" proved="true" arg1="H7" arg2="x,y">
     <goal name="VC lrs.20.0.0" expl="postcondition" proved="true">
-    <transf name="instantiate" proved="true" arg1="Hinst" arg2="y">
-     <goal name="VC lrs.20.0.0.0" expl="postcondition" proved="true">
-     <proof prover="2"><result status="valid" time="0.04"/></proof>
-     </goal>
-    </transf>
+    <proof prover="2"><result status="valid" time="0.04"/></proof>
     </goal>
    </transf>
    </goal>

src/parser/parser.mly

@@ -1307,6 +1307,7 @@ qualid_comma_list_eof:
 ident_comma_list_eof:
 | comma_list1(ident) EOF { $1 }
 
-(* TODO: Weird to not have any parser conflicts here *)
 term_comma_list_eof:
-| comma_list1(term) EOF { $1 }
+| comma_list1(single_term) EOF { $1 }
+(* we use single_term to avoid conflict with tuples, that
+   do not need parentheses *)