[RFC - Python Scripting] New method gdb.Symtab.blocks_iterator - docs included

[Eli Zaretskii]

> Date: Tue, 10 Apr 2012 00:04:10 +0530
> From: Siva Chandra <sivachandra@google.com>
> 
> While the work on Objfile.symtabs (or Objfile.iterator) is pending, I
> want to complete the API for the exploratory path Objfile => Symtabs
> => Blocks => Symbols.  This patch adds the missing link Symtabs =>
> Blocks.  The method Symtab.blocks_iterator returns an iterator to
> iterate over the scope blocks of a symtab.  The patch is attached

Thanks, the documentation parts of this patch are approved.