cv_configlet : fix bugs where some configlet with small changes were not updated

[b-abadie]

This fixes #135

This PR fixes two bugs (one confirmed, and one suspected):

• The usage of quick_ratio() can sometimes return 1.0 (i.e. no difference between current version and desired version) when changes are very small. In fact, the documentation specifies that this function is faster but only returns an upper bound instead of the actual value. This PR fixes the bug by using ratio() instead.
• This is a suspected bug : by rounding the returned ratio, a very large configlet with a very small change could be considered unchanged. This PR removes the rounding (and the transformation to a percentage that seems useless to me).