Remove creation of redundant function nodes

qdoc creates a function node each time it parses a function declaration, even when it is parsing a function definition in a .cpp file or a \fn command. qdoc should only create function nodes when it is parsing .h files, and possibly in a few other cases. When qdoc sees a function definition or \fn command in a .cpp file, it should avoid creating a function node, because qdoc already created it when it parsed the function declaration in a .h file.

Additionally, the "No documentation for..." error should include the parameters when the error refers to a function without documentation.