Support linbox 1.7.0 and 1.6.3 at the same time

The constructor `DenseMatrix(field, entries, m, n)` in 1.6.3 was changed
to `DenseMatrix(field, m, n, entries)` in 1.7.0.

We replace use of this constructor by a different way to initialize a
matrix from entries using part of the API that works both in 1.6.3 and
in 1.7.0.

Note that the two versions of the library are still ABI-incompatible so
changing linbox requires recompiling sagelib. To complicate matters,
linbox doesn't change soname so the dynamic linker will let this go and
sagemath will eventually crash.

Author: tornaria

src/sage/libs/linbox/linbox.pxd

@@ -32,7 +32,6 @@ cdef extern from "linbox/matrix/dense-matrix.h":
         ctypedef Modular_double Field
         ctypedef double Element
         DenseMatrix_Modular_double(Field F, size_t m, size_t n)
-        DenseMatrix_Modular_double(Field F, size_t m, size_t n, Element*)
         void setEntry(size_t i, size_t j, Element& a)
         Element &getEntry(size_t i, size_t j)
 
@@ -42,7 +41,6 @@ cdef extern from "linbox/matrix/dense-matrix.h":
         ctypedef Modular_float Field
         ctypedef float Element
         DenseMatrix_Modular_float(Field F, size_t m, size_t n)
-        DenseMatrix_Modular_float(Field F, size_t m, size_t n, Element*)
         void setEntry(size_t i, size_t j, Element& a)
         Element &getEntry(size_t i, size_t j)
 

src/sage/matrix/matrix_modn_dense_template.pxi

@@ -221,9 +221,14 @@ cdef inline linbox_echelonize_efd(celement modulus, celement* entries, Py_ssize_
         return 0,[]
 
     cdef ModField *F = new ModField(<long>modulus)
-    cdef DenseMatrix *A = new DenseMatrix(F[0], <Py_ssize_t>nrows, <Py_ssize_t>ncols, <ModField.Element*>entries)
-    cdef Py_ssize_t r = reducedRowEchelonize(A[0])
+    cdef DenseMatrix *A = new DenseMatrix(F[0], nrows, ncols)
+
     cdef Py_ssize_t i,j
+    for i in range(nrows):
+        for j in range(ncols):
+            A.setEntry(i, j, entries[i*ncols+j])
+
+    cdef Py_ssize_t r = reducedRowEchelonize(A[0])
     for i in range(nrows):
         for j in range(ncols):
             entries[i*ncols+j] = <celement>A.getEntry(i,j)