Start with switch to C++03.

Start switching some code to C++03, with defaulted/deleted constructors
and unique_str to auto_ptr in some header files.
Switch gui/widgets/credentials over to C++03.

Replace lambda expression in gui/widgets/credentials.cpp with Functor
class so that the code compiles in C++03 mode.
Switch Namecoin code over to C++03.
Compile with C++03 flags by default.