Undo commit if travis-ci fails with this

- this commit uses a wrong filename for doxygen exceptions, i.e., the `make doc` should fail on travis-ci because it will find doxygen warnings

- if indeed, travis-ci fails with this commit, then our continuous integration checks pass both positive and negative cases correctly

tools/run_doxygen.sh

@@ -16,7 +16,7 @@ doc_path="doc"                            # path to documentation
 doxy=${doc_path}"/Doxyfile"               # Doxyfile
 log=${doc_path}"/log_doxygen.log"         # logfile for doxygen output
 log_tmp=${doc_path}"/log_doxygen_tmp.log"
-doxexcept=${doc_path}"/doxygen_exceptions.txt" # filename that lists exceptions (one per line)
+doxexcept=${doc_path}"/doxygen_exceptions_wrong.txt" # filename that lists exceptions (one per line)
 
 # Downgrade Doxyfile in case this runs an old doxygen version, e.g.,
 # travis-ci is currently on 1.8.6 (instead of 1.8.15)