support seperating expressons by ;

support seperating expressons by ;
support variables, the syntax isnt beautifull (st(a,b) means var[a]=b and ld(a) var[a]) but for a mere 19 lines of code its fairly simple, if anyone wants to write real variables support with names for variables and = and [] then that would of course be welcome but only if it doesnt bloat the code up terribly...)

Originally committed as revision 6813 to svn://svn.ffmpeg.org/ffmpeg/trunk