Adjust Doxygen comments.

Cherry-picked changes, left out white-space changes
and variable renaming, from 36cebfb6d30703a9db4253e4ca4f7d7f3b4e92d3

Signed-off-by: Christoph Grüninger <gruenich@dune-project.org>

dune/istl/umfpack.hh

@@ -209,7 +209,7 @@ namespace Dune {
      * This computes the matrix decomposition, and may take a long time
      * (and use a lot of memory).
      *
-     *  @param mat_ the matrix to solve for
+     *  @param matrix the matrix to solve for
      *  @param verbose [0..2] set the verbosity level, defaults to 0
      */
     UMFPack(const Matrix& matrix, int verbose=0) : matrixIsLoaded_(false)
@@ -227,7 +227,7 @@ namespace Dune {
      * This computes the matrix decomposition, and may take a long time
      * (and use a lot of memory).
      *
-     * @param mat_ the matrix to solve for
+     * @param matrix the matrix to solve for
      * @param verbose [0..2] set the verbosity level, defaults to 0
      */
     UMFPack(const Matrix& matrix, int verbose, bool) : matrixIsLoaded_(false)