Name mangling robustness

[jkotas]

Make name mangling to be robust against collisions with built-in C++ identifiers or our internal identifiers (see #31)

[manu-st]

Does this cover the case where the following C++ code is generated:

namespace A { namespace A {...

It confuses the C++ compiler whenever you use later A::A?

[jkotas]

This case should be tracked by CppCodeGen specific issues (#122).

[jkotas]

Let's track this in #2178