Use @pyregion when loading Python objects from arrays (#843)

This branch calls incref(u) to increment the objects refcount, which without
@pyregion would be a data race if other threads accessed it at the same time.

Author: JamesWrigley

src/Wrap/PyArray.jl

@@ -652,9 +652,11 @@ function pyarray_load(::Type{T}, p::Ptr{R}) where {T,R}
     if R == T
         unsafe_load(p)
     elseif R == C.PyPtr
-        u = unsafe_load(p)
-        o = u == C_NULL ? pynew(Py(nothing)) : pynew(incref(u))
-        T == Py ? o : pyconvert(T, o)
+        @pyregion begin
+            u = unsafe_load(p)
+            o = u == C_NULL ? pynew(Py(nothing)) : pynew(incref(u))
+            T == Py ? o : pyconvert(T, o)
+        end
     else
         convert(T, unsafe_load(p))
     end