FileName is a small utility, used for building good filename paths
with respect to the File.Separator used by de operating system.
The arguments for the constructors will be glued together by File separators.
String docfilename = new FileName(a, b, c).toString();
will result in : docfilename == a/b/c on a unix filesystem.
This method gets an if-tag and depending on the expression returns a block
if if-expr=true --> first block (item(0))
if if-expr=false --> second block if any (item((1))
The method redirect will be called by child servlets if
their call to super.initService(request, response) throws an error
The user will get an error message on his screen