Fix C usage of pstoedit.h
    
    The loadpstoeditplugins declaration in 4.00 pstoedit.h includes
    std::ostream and bool parameters, which are only compatible with C++.
    When building autotrace with pstoedit-4.00, the build fails as a result.
    
    Reported upstream: https://sourceforge.net/p/pstoedit/patches/5/