fix 2 bugs in quartic equation solver routine from A. Steiner and A. Buckley  - protect against  wrong input to acos due to numerical errors was   - remove assignement u[2]=u[1] as in CERNLIB routine. The gsl cubic solver is used and therefore a different order of the roots is returned. 
fix 2 bugs in quartic equation solver routine from A. Steiner and A. Buckley
 - protect against  wrong input to acos due to numerical errors was 
 - remove assignement u[2]=u[1] as in CERNLIB routine. The gsl cubic solver is used and therefore a different order of the roots is returned. 

This fixes the bug reported in https://savannah.cern.ch/bugs/?49031


git-svn-id: acec3fd5b7ea1eb9e79d6329d318e8118ee2e14f@28158 27541ba8-7e3a-0410-8455-c3a389f83636

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