This is only usefull for rotate now, but the axis constraining code has a part that depended on this, so I commit this part first.
For coders:
void constline(float *center, float *dir, int col)
Draw an infinite line on the screen. col is the color argument. It must be cpack compatible
void project_short_infiniteline(float *vec, float *dir, short *adr1, short *adr2);
clips infinite line to screen border