Change the suffix for reinstalled eups products from a,b,c,... to +a,+b,+c,....

When we reinstall a given product version on top of updated dependencies, we append a single letter onto the version string. This fails to order correctly using both the "standard" python number scheme and the eups one.

Change the suffix to "+a", "+b", etc, which is handled correctly by, say, pkg_resources.package.version [ Check against the eups version scheme first, adapt if necessary. ]