Better signature for copy constructors.

[Thierry Delisle]

Copy constructors now have a weird C copy as a parameter. This is due to historical reasons and should use const reference instead.

I.e. this:

void ?{} (int&, const int&);
int& ?=? (int&, const int&); 

Instead of

void ?{} (int&, int);
int& ?=? (int&, int);