deletes a file
f = deletefile(filename)
This function deletes a file. If file has been deleted, it will return %t else %f.
fd = `mopen`_(TMPDIR+'/filetodelete.txt','wt');
`mclose`_(fd);
if (`fileinfo`_(TMPDIR+'/filetodelete.txt') <> []) then
deletefile(TMPDIR+'/filetodelete.txt')
end
deletefile(TMPDIR+'/notexistingfile')