Fix performance bug in std.find implementation
Fix performance bug in std.find implementation

It turns out std::string::find is way slower than strstr... Thanks to g
webb for spotting this!

pombredanne/pythran,hainm/pythran,pombredanne/pythran,pombredanne/pythran,artas360/pythran,serge-sans-paille/pythran,serge-sans-paille/pythran,artas360/pythran,pbrunet/pythran,pbrunet/pythran,hainm/pythran,pbrunet/pythran,hainm/pythran,artas360/pythran