prepare for version 0.014
prevent warning message in test output
disallow empty piddles when processing

This should fix the warning message I started receiving with recent
development versions of PDL (2.007_01 or maybe 2.007_02), in which an
empty piddle in one of the tests led to ->min() and ->max() containing
the string 'BAD' which raised a warning in numerical comparisons and
hence made the test suite fail.
update Changes
v0.014

 - tests started failing with recent development versions of PDL (2.007_01 or
   2.007_02, not sure). Fixed now. (Edward Baudrez)