boost pulled in from gexiv2 fails for python target

[rmottola (Riccardo)]

upgrade wants to pull in gexiv2:

The following ports will be rebuilt:
 gexiv2 @0.10.8+python27+python36
 gimp2 @2.10.6+python27+quartz

gexiv2 pulls in boost, a port which I do not have yet installed, however it fails:

Error: boost: Variant python27 conflicts with python36
Error: Unable to open port: Error evaluating variants
Error: rev-upgrade failed: Error rebuilding gexiv2

[ryandesign (Ryan Carsten Schmidt)]

The gexiv2 port intentionally allows one python2x and one python3x variant to be selected. However the boost port intentionally allows only one python variant to be selected regardless of version.

MacPorts passes variant selections (apparently regardless of how the variant selection was supplied—by you on the command line, or in your variants.conf, or by a port in its default_variants) down to any dependencies that are not yet installed.

Clean boost and install it with only one python variant of your choice.

[rmottola (Riccardo)]

Once done, it works. This is incovenient because it needs manual intervention during upgrades, but works. The bug can be closed for me if there is no way to make it "auto".