Read/write portage revisions in ebuild filenames

[hololeap]

Currently, hackport will overwrite an ebuild if it shares the same version as what it is grabbing from Hackage. For instance, this will overwrite diagrams-svg.1.4.3.1.ebuild if it already exists

$ hackport merge diagrams-svg-1.4.3.1
...
Writing diagrams-svg-1.4.3.1.ebuild

This may sometimes be the preferable option, as it may not be necessary to cause rebuilds for the package in question if it is a very minor update (for instance EAPI or DEPENDS). However, often times a portage revision bump is desirable, so in this case it should write diagrams-svg-1.4.3.1-r1.ebuild.

Similarly, a revision for the version in question may already exist. In this case, hackport will still output an ebuild without any revision number, which requires the developer to manually rename it. For instance, if diagrams-svg-1.4.3.1-r2.ebuild already existed, it would output to diagrams-svg-1.4.3.1.ebuild instead of a -r2 or -r3 ebuild.

It would be convenient if hackport:

1. recognized portage revisions and knew how to create a revision bump or overwrite an existing revision
2. contained some logic of when it should create a revision bump vs. overwriting

[hololeap]

If #2 isn't feasible, then it should just default to creating a revision bump every time and let the developer decide if they want to rename it back to the previous revision.