Use imag, real, arg from std library for Complex types. * lo-mappers.h (imag, real, arg): Delete overloaded functions from octave::math namespace. Add comment about why overload for conj must remain (different behavior desired than prototype under C++). * ls-mat4.cc, ls-mat5.cc, mgorth.cc, ov-cx-mat.cc, ov-cx-sparse.cc, ov-float.cc, ov-flt-cx-mat.cc, ov-flt-re-mat.cc, ov-re-mat.cc, ov-re-sparse.cc, ov-scalar.cc, CMatrix.cc, CSparse.cc, MatrixType.cc, dMatrix.cc, dSparse.cc, fCMatrix.cc, fMatrix.cc, chol.cc, eigs-base.cc: Replace calls to octave::math::XXX with std::XXX for imag, real, and arg.

--- a/libinterp/corefcn/mgorth.cc	Tue Jun 27 07:57:52 2017 -0400
+++ b/libinterp/corefcn/mgorth.cc	Tue Jun 27 09:24:08 2017 -0700
@@ -44,7 +44,7 @@
     }
 
   h(Vc) = xnorm (x);
-  if (octave::math::real (h(Vc)) > 0)
+  if (std::real (h(Vc)) > 0)
     x /= h(Vc);
 }