Avoid symmetrizing diagonal in hermitian power (#1321)

This would make these operations work with immutable matrices as well.
The `Hermitian` wrapper ensures that the result has a real diagonal.

Author: jishnub

src/symmetric.jl

@@ -866,24 +866,14 @@ function ^(A::Hermitian, p::Integer)
     else
         retmat = Base.power_by_squaring(A, p)
     end
-    for i in diagind(retmat, IndexStyle(retmat))
-        retmat[i] = real(retmat[i])
-    end
     return Hermitian(retmat)
 end
 function ^(A::Hermitian{T}, p::Real) where T
     isinteger(p) && return integerpow(A, p)
     F = eigen(A)
     if all(λ -> λ ≥ 0, F.values)
         retmat = (F.vectors * Diagonal((F.values).^p)) * F.vectors'
-        if T <: Real
-            return Hermitian(retmat)
-        else
-            for i in diagind(retmat, IndexStyle(retmat))
-                retmat[i] = real(retmat[i])
-            end
-            return Hermitian(retmat)
-        end
+        return Hermitian(retmat)
     else
         retmat = (F.vectors * Diagonal((complex.(F.values).^p))) * F.vectors'
         if T <: Real