When decorating a function without changing the signature, it 
is generally appropriate to preserve the metadata from original 
function. 
 
This currently involves copying the docstring and name and 
updating the function attribute dict manually. 
 
This patch adds an "update_meta" method to function objects 
which modifies the current function to masquerade as the 
original function. 
 
Test & documentation patches still to come. (Although the 
docstring text could also be used for the documentation)