Optimization: class.is-a

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-12-23 03:46:02

The class.is-a method was called many times. In two cases, it was 
debug/diagnostic code which is not really needed and in yet another place, 
using type.is-derived was sufficient.

Performance.
Femtown (reference Boost.Build)
Real: min 16:590, max 17:330, avg 16:926
User: min 15:510, max 15:660, avg 15:573

Femtown (CVS Boost.Build)
Real: min 15:830, max 16:360, avg 16:13
User: min 14:700, max 15:70, avg 14:830

TBLib (reference Boost.Build)
Real: min 8:790, max 9:630, avg 9:270
User: min 8:410, max 8:820, avg 8:660

TBLib (CVS Boost.Build)
Real: min 8:530, max 9:50, avg 8:860
User: min 8:310, max 8:490, avg 8:420