Search explicitly for libgul14 which is required by DOOCS libraries

Removed libtine linking workaround from FindDOOCS. Doocs libraries now are themselves linked correctly against tine.

This confused git massively

The pkg-config file is missing so we have to search for the library
manually

This is a work-around for libDOOCSapi linking against it but expecting
/export/doocs/lib to be in the linker search path (not using rpath)

May be reverted once/if doocs fixes this

FindDOOCS: extend PKG_CONFIG_PATH by directory set via DOOCS_DIR (if set) and the hardcoded default in /export/doocs/...

usage:
register_tests(SOURCES
                 ${list_of_source_files}
                 "test_src.cc"
                 ${concatenated_string_of_source_files}
               NAMESPACE
                 "test_namespace"
               LINK_LIBRARIES
                 ${list_of_targets}
               INCLUDE_DIRECTORIES
                 ${list_of_include_directories}
               COMPILE_OPTIONS
                 ${list_of_compile_options}
               WORKING_DIRECTORY
                 ${ctest_working_directory})

new scheme:
register_tests(SOURCES
                 ${list_of_source_files}
                 "test_src.cc"
                 ${concatenated_string_of_source_files}
               NAMESPACE
                 "test_namespace"
               LINK_LIBRARIES
                 ${list_of_targets}
               INCLUDE_DIRECTORIES
                 ${list_of_include_directories}
               COMPILE_OPTIONS
                 ${list_of_compile_options})

usage:
register_tests(SOURCES
                 ${list_of_source_files}
                 "test_src.cc"
                 ${concatenated_string_of_source_files}
               NAMESPACE
                 "test_namespace"
               DEPENDS
                 ${list_of_targets}
               INCLUDES
                 ${list_of_include_directories}
               COMPILE_OPTIONS
                 ${list_of_compile_options})

Function registers tests defined as a list of souce files.  Test defined
by file source_name.cc in the SOURCES list is registered under the name
  test_namespace.source_name

Provided list of dependent targets and include directories are used for
test executables as PRIVATE dependencies during compilation.

Function implicitly adds a dependency on the boost unit test framework
to each generated test executable.

Fixed the confusing and inconsistently used names *_LINK_FLAGS and *_LINKER_FLAGS by always setting and getting both variables

added TINE_EXPORT C macro/constant to the compiler flags, which seens to be required for the latest DOOCS version

need to find DOOCS_DIR first, since this is the variable which might be specified at the cmake command line