Change deprecated 'ftools' to 'fileutils'.

'ftools' only work on Ruby 1.8, while 'fileutils' works on Ruby 1.8 and 1.9.

I don't know how far back in 1.8 'fileutils' is avaiable -- would need to check if it's a problem for 1.8.6 or 1.8.5, if you still support those?