[boost] [shifted_ptr] Updated thread and <const T> support

From: Phil Bouchard (philippe_at_[hidden])
Date: 2008-04-13 17:49:05

Greetings:

Upon testing the library on day to day projects, support for <const T> 
objects is invaluable and thus was added.  Support for volatile objects 
could be important in certain cases also but requires more overloaded 
functions to be added (const ^2 + volatile ^2).

Furthermore I have changed the code to use the new thread_specific_ptr<> 
object handler but I have disabled it by default with 
BOOST_SH_DISABLE_THREADS.

Thanks,
-Phil