last stab at alternative pointer support

[Bob Walters <bob dot s dot walters at gmail dot com>]

Final stab at alternative pointer support.  This should be 100% ABI  
compatible for all existing instances of _Rb_tree and it's associated  
iterators, for which Alloc::pointer is any standard pointer type.   
Considering that the library doesn't current support non-standard ones  
I hope that's enough.

To achieve this I preserved the existing types by duplicating the code  
for the iterator and node types.  The iterators and the _Rb_tree  
itself should be ABI compatible if passed between old/new versions of  
the code.  I'll confirm this with a test if desired.  A look over the  
changes will show that with a standard pointer, the instantiated code  
for _Rb_tree looks like the original (hence the ABI compatibility).   
All of the new parameterized types come into play only when the _Alloc  
parameter yields a non-standard pointer type.

Attachment: patch_stl_tree_h.txt
Description: Text document

Attachment: stl_tree.tcc
Description: Binary data

Bob