dirname - trip last component from file name
string dirname -> string
(./../test/dir/foo.sli) dirname -> (./../test/dir)
Print NAME with its trailing /component removed;
if NAME contains no /'s, output `.' (meaning the current directory).
string: Name of the directory
Yury V. Zaytsev and Jochen M. Eppler
November 2012
/var/www/debian/nest/nest-simulator-2.20.0/lib/sli/filesystem.sli