Don't swap function decls, and add them to the scope as they are

encountered.  Mixing up the decls is unintuitive, and confuses the AST 
destruction code. Fixes PR2360.

Note that there is a need to look up the characteristics and 
declarations of a function associated with a particular name or decl, 
but the original swapping code doesn't solve it properly. 
http://lists.cs.uiuc.edu/pipermail/cfe-dev/2008-May/001644.html is one 
suggestion for how to fix that.

llvm-svn: 51584