fix compilation with g++, extern inline vs. static inline

Hi,

I have a problem build multimonNG in QtCreator, identifiet the problem and created a fix.

I fixed only what was immediate broken, there are other few lines with 'extern inline' whitch i left untouched.

'extern' and 'inline' cannot be combined (in g++ 4.7) together in this manner
and do not make sense either. Rather use 'static inline' which makes
the function inline, but does not export it in resulting *.o so no
symbol redefinition occurs.