When doing << or >> operators, don't convert the return type to the type of the shift amount.

Fixes issue #73.  Previously, if we had e.g. an int16 type that was being shifted
left by 1, then the constant integer 1 would come in as an int32, we'd convert
the int16 to an int32, and then we'd do the shift.  Now, for shifts, the type
of the expression is always the same as the type of the value being shifted.

expr.h

@@ -97,7 +97,7 @@ public:
         that incorporates the given error message string.  In either
         failure case, NULL is returned.  */
     Expr *TypeConv(const Type *type, const char *errorMsgBase = NULL, 
-                   bool failureOk = false);
+                   bool failureOk = false, bool issuePrecisionWarnings = true);
 };