Predicated 'if' statement performance improvements.

Go back to running both sides of 'if' statements with masking and without
branching if we can determine that the code is relatively simple (as per
the simple cost model), and is safe to run even if the mask is 'all off'.
This gives a bit of a performance improvement for some of the examples
(most notably, the ray tracer), and is the code that one wants generated
in this case anyhow.

stmt.h

@@ -77,7 +77,6 @@ public:
     Stmt *TypeCheck();
     int EstimateCost() const;
 
-private:
     Expr *expr;
 };
 
@@ -95,7 +94,6 @@ public:
     Stmt *TypeCheck();
     int EstimateCost() const;
 
- private:
     Declaration *declaration;
 };
 
@@ -156,7 +154,6 @@ public:
     Stmt *TypeCheck();
     int EstimateCost() const;
 
-private:
     Expr *testExpr;
     Stmt *bodyStmts;
     const bool doCoherentCheck;
@@ -178,7 +175,6 @@ public:
     Stmt *TypeCheck();
     int EstimateCost() const;
 
-private:
     /** 'for' statment initializer; may be NULL, indicating no intitializer */
     Stmt *init;
     /** expression that returns a value indicating whether the loop should
@@ -250,7 +246,6 @@ public:
     Stmt *TypeCheck();
     int EstimateCost() const;
 
-private:
     Expr *val;
     /** This indicates whether the generated code will check to see if no
         more program instances are currently running after the return, in
@@ -301,7 +296,6 @@ public:
     Stmt *TypeCheck();
     int EstimateCost() const;
 
-private:
     /** Format string for the print() statement. */
     const std::string format;
     /** This holds the arguments passed to the print() statement.  If more