Fixup comments

Author: sandersn

src/compiler/checker.ts

@@ -7978,7 +7978,7 @@ namespace ts {
             }
             // An instance property must be accessed through an instance of the enclosing class
             if (type.flags & TypeFlags.ThisType) {
-                // get the original type -- represented as the type constraint of the this type
+                // get the original type -- represented as the type constraint of the 'this' type
                 type = getConstraintOfTypeParameter(<TypeParameter>type);
             }
 

src/services/services.ts

@@ -4106,7 +4106,8 @@ namespace ts {
                         let allSignatures = useConstructSignatures ? type.getConstructSignatures() : type.getCallSignatures();
 
                         if (!contains(allSignatures, signature.target) && !contains(allSignatures, signature)) {
-                            // Get the first signature if there
+                            // Get the first signature if there is one -- allSignatures may contain
+                            // either the original signature or its target, so check for either
                             signature = allSignatures.length ? allSignatures[0] : undefined;
                         }