Building igl statically and moving to the dep scripts

Fixing dep build script on Windows and removing some warnings.

Use bundled igl by default.

Not building with the dependency scripts if not explicitly stated. This way, it will stay in
Fix the libigl patch to include C source files in header only mode.

src/libigl/igl/isdiag.h

@@ -0,0 +1,26 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+// 
+// Copyright (C) 2016 Alec Jacobson <alecjacobson@gmail.com>
+// 
+// This Source Code Form is subject to the terms of the Mozilla Public License 
+// v. 2.0. If a copy of the MPL was not distributed with this file, You can 
+// obtain one at http://mozilla.org/MPL/2.0/.
+#ifndef IGL_ISDIAG_H
+#define IGL_ISDIAG_H
+#include "igl_inline.h"
+#include <Eigen/Sparse>
+namespace igl
+{
+  // Determine if a given matrix is diagonal: all non-zeros lie on the
+  // main diagonal.
+  //
+  // Inputs:
+  //   A  m by n sparse matrix
+  // Returns true iff and only if the matrix is diagonal.
+  template <typename Scalar>
+  IGL_INLINE bool isdiag(const Eigen::SparseMatrix<Scalar> & A);
+};
+#ifndef IGL_STATIC_LIBRARY
+#  include "isdiag.cpp"
+#endif
+#endif