Bug 719591 - expand_as_defined macro does not properly work

    read \ref unix_problems "this section" first.

<li>Doxygen is <em>not</em> a real compiler, it is only a lexical scanner.

    This means that it can and will not detect errors in your source code.

<li>Doxygen has a build in preprocessor, but this works slightly different than

    the C preprocessor. Doxygen assumes a header file is properly guarded against

    multiple inclusion, and that each include file is standalone (i.e. it could be placed

    at the top of a source file without causing compiler errors). As long as this is

    true (and this is a good design practice) you should not encounter problems.

<li>Since it is impossible to test all possible code fragments, it is

    very well possible, that some valid piece of C/C++ code is not handled

    properly. If you find such a piece, please send it to me, so I can