Use new annotation history feature of zc.buildout

[jensens]

buildout -v annotate shows the history of a single value in a a section. This can be accessed by buildout._annotated[buildout['buildout']['versions']][EGGNAME].history. This was added by Godefroid

This is a bigger refactoring but worth the effort.

[loechel]

in the 2.0 branch ther is already something similar, that accesses all buildout internal varaibales and history

[jensens]

But the approach here saves us lots of trouble and complexity. must not be refactored now, but I'll do at some point.