big huge changes, so i dont remember everything.

* renaming, e.g. LU ---> FullPivLU
* split tests framework: more robust, e.g. dont generate empty tests if a number is skipped
* make all remaining tests use that splitting, as needed.
* Fix 4x4 inversion (see stable branch)
* Transform::inverse() and geo_transform test : adapt to new inverse() API, it was also trying to instantiate inverse() for 3x4 matrices.
* CMakeLists: more robust regexp to parse the version number
* misc fixes in unit tests

doc/snippets/FullPivLU_kernel.cpp

@@ -0,0 +1,7 @@
+MatrixXf m = MatrixXf::Random(3,5);
+cout << "Here is the matrix m:" << endl << m << endl;
+MatrixXf ker = m.lu().kernel();
+cout << "Here is a matrix whose columns form a basis of the kernel of m:"
+     << endl << ker << endl;
+cout << "By definition of the kernel, m*ker is zero:"
+     << endl << m*ker << endl;