Simple stepper motor circuit safe?
the ULN2803A has already lots of protection diodes.. safe enough?
  


Yes. 


  
  the Mitsumi M55SP-1N datasheet says 259mA/phase*4=1,1Amp..correct?
  


Yes (close enough). The resistance of each phase is 50&ohm; +-7%, so at 12V it should draw approximately 12/50 = 240mA per phase (actually it should be even less than this, due to voltage drop in the Darlington transistors).   


  
  powersupply of 1.25 Ampere....enough right?
  


Yes.


  A strange thing happend .. @5v with high speed stepping the ULN2803A got 
  hot.
  50-60 deg C. normal?


Getting hot at high speed is to be expected. Each time a coil is turned off the flyback diode passes a pulse of current as the magnetic field in the coil dissipates. At high speed the diodes pass as much current when the coils are turned off as the transistors do when they are turned on, which increases total power loss. The transistors also have a switching loss which becomes more significant as stepping speed increases.      

50-60&deg; case temperature is OK. The ULN2803 is not very efficient. At 240mA each Darlington transistor drops about 1.1V, which equates to 1.1W of total power loss when all 4 phases are turned on. Maximum allowed junction temperature is 125&deg;C. Junction to Ambient thermal resistance is 73&deg;C/Watt (D package), so at room temperature (20&deg;C) and 1.1W the junction temperature should be ~100&deg;C.      


  uln2803 handles 500mA per channel and a max of 2,5A ....


Those are absolute maximum stress ratings, not recommended for normal operation. For safety and reliability you should not exceed half those values.