Exclude is the correct term to use when removing paths from the
list of checked items. Ignore as a term was a poor choise to begin
with. XML file reading still recognizes and reads the 'ignore'
element but writes 'exclude' element.
Ticket: #2995 (GUI: Rename ignore-feature to exclude-feature)
The 'test/test.cxx' is a test file that contains some errors for
testing purposes. Exclude it from the GUI-project file used to
check Cppcheck sources so people don't report errors from it.