Hotfix finish does not check for pending commits

[petersondrew]

The bash version of gitflow does not allow hotfixes (and I'm guessing features and releases) to be finished while there are uncommitted changes.
I feel that's an important safety net to have, could we get that same feature in the python version?

[htgoebel]

For hotfix and release I'd aggree. For feature I'm unsure and would like to mimic the bash-version.

Please submit a pull-request or at least point me to what needs to be changed.