* arts-2-1-497

* src/file.cc (file_exists):

Was falsely returning true if the given file was a directory.
Led to a segfault if controlfile contained e.g. INCLUDE "general"

git-svn-id: https://www.sat.ltu.se/svn/rt/arts/trunk@8187 aaf1aab0-4228-0410-ad68-8dceda47f409
* arts-2-1-498

* Add support for testcases that depend on arts-xml-data. cmake will
look for a-x-d in the same path as the arts source or at a custom
location specified by the user with:

cmake -DARTS_XML_DATA_PATH=/home/myname/arts-xml-data ..

If a-x-d is not found, tests depending on it will not be run.

Look at the bottom of controlfiles/CMakeLists.txt for an example on
how to define testcases that need a-x-d.

* CMakeLists.txt: Add support for ARTS_XML_DATA_PATH.

* cmake/modules/ArtsTestcases.cmake:

Add -D option to arts call if arts-xml-data path is defined.

* controlfiles/CMakeLists.txt: Add example for a-x-d dependency.

* README: Updated with info about ARTS_XML_DATA_PATH.

git-svn-id: https://www.sat.ltu.se/svn/rt/arts/trunk@8188 aaf1aab0-4228-0410-ad68-8dceda47f409