Add support for copytruncate style logrotation

If original file is still same inode, but size is smaller check for
rotation candidates. Some programs require this style of rotation.
Added as a option to prevent any unexpected behaviour.
Adding test cases for copytruncate.

Included expected behaviour for when copytruncate support is disabled.
Merge pull request #11 from atward/copytruncate

Add support for copytruncate style logrotation