C++ function signature: Allow most specifiers to be replaced.

Except for some SimpleSpecifiers and AttributeSpecifiers. Fixes a bug
where NamedTypeSpecifiers would not be replaced when the return type
was adjusted.

Change-Id: Ie093615ebf1b26d181b888fcbcc341e5bdf85fd1
Reviewed-on: http://codereview.qt-project.org/4749


Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>