Recompute unbranched argument in principal_branch
Recompute unbranched argument in principal_branch

principal_branch removes polar_lift from symbols. In some cases
this will result in wrong answer.

>>> b = Symbol('b', negative=True)
>>> e = exp_polar(-pi*I/2)/polar_lift(b)
>>> unbranched_argument(e)
-3*pi/2
>>> principal_branch(e, 2*pi)
exp_polar(3*I*pi/2)/b
>>> unbranched_argument(_)
5*pi/2  # this should be -3*pi/2 + 2*pi = pi/2

In this commit, unbranched argument is recomputed after polar_lift
has been removed from symbols.

>>> principal_branch(e, 2*pi)
exp_polar(-I*pi/2)/b
>>> unbranched_argument(_)
pi/2

kaushik94/sympy,kaushik94/sympy,kaushik94/sympy