Further actions to make MatrixFree/FEEvaluation work in 1D

- Added test for matrix-vector product
- Made compile with clang.
Merge pull request #221 from kronbichler/master

Fix a compiler warning with gcc-4.9. 
gcc-4.9 seems to be able to see that accessing R[1] in 1D is out of bound
for spacedim == 1 but it can omit the warning if accessed inside a switch
statement. Fix this warning (even though we won't use SphericalManifold
for spacedim == 1).
Merge pull request #222 from kronbichler/matrix_free_1d

Further actions to make MatrixFree/FEEvaluation work in 1D
Update the documentation about requiring at least Trilinos 11.2
Merge pull request #220 from Rombur/trilinos_11_2

Update the documentation about requiring at least Trilinos 11.2
Fix an oversight that prevented code from compiling.
Remove a broken link.
Merge pull request #224 from bangerth/fix-compile-error

Fix an oversight that prevented code from compiling.
Merge pull request #225 from bangerth/remove-broken-link-2

Remove a broken link.
Adjust tests that fail due to vectorized accumulation

Commit c7f3054 changed the order of summation in inner products and norms because
these operations are now done in vectorized form. The affected tests show spurious
changes in the last digit.

To improve, the following changes were made:
- error_estimator_0?: The output was scaled by l1 norm which is unsafe. These tests
  should only test error estimation and hence the scaling is done by linfty_norm
  which will never depend on roundoff. Note that we output up to 7 digits of a float
  which notoriously runs into roundoff issues.
- mesh_3d_12 also outputs 6-7 digits of a float. Changed the accuray of output to 5
  digits.
- q_dg0_projection was deleted because it FE_Q_DG0 has a singular mass matrix and thus
  the final solution on the face can be anything. Note e.g. how different the previous
  solutions for Intel/non-Intel compilers were -> no good test.