Trac #16943: convert angle_label to float if possible
Trac #16943: FiniteStateMachine._latex_: convert angles to floats where necessary.

Fix the following bug:
{{{
sage: T = Transducer([(0,1),(1,1),(2,2),(3,3),(4,4)])
sage: latex(T)
Traceback (most recent call last)
...
TypeError: float argument required, not
sage.symbolic.expression.Expression
}}}

URL: http://trac.sagemath.org/16943
Reported by: cheuberg
Ticket author(s): Clemens Heuberger
Reviewer(s): Sara Kropf