Loosen version requirements

This is a pull request to close gh-5.
It is checked by perl-5.8.9 with Test::More 0.80, using perlbrew.

Additionally, the following modifications are included.
- I forgot to add test cases for eval BLOCK in gh-4. Now, the test cases are added.
- The current logic can't handle correctly nested BLOCK without semicolon terminator at the end like ```eval { { use Test::Pod } use Test::Pod::Coverage }``` while ```eval { { use Test::Pod; } use Test::Pod::Coverage }``` can be handled.  I hope this case is rare, so I add the case to 80-failing.t and leave the behavior as it is.