[sqrt] better estimate lifting bound in algebraic square root
Imported issue: Initially reported by @zimmerma in https://gforge.inria.fr/tracker/?group_id=2065&aid=14675
currently in sqrt.c, function polymodF_sqrt(), we estimate the lifting bound to half of the maximal coefficient size,
plus 10% (thus 55% of the maximal coefficient size).
In crtalgsqrt.c a more accurate estimation is computed by the function estimate_nbits_sqrt.
We should try this estimate in sqrt.c.
Paul