Upgrade macro imports to pythonic semantics

[Technologicat]

To deal with name conflicts in macro imports, the least surprise requires that we follow Python's regular import semantics (latest definition of a particular name wins).

So we should upgrade both consoles to behave that way. This allows shortening the explanation.

MacroPy's detect_macros() has no side effects other than triggering imports, so we can manage the macro bindings ourselves. The bindings are held in the object we hand to the macro expander.

[Technologicat]

This issue is resolved in the third-generation macro expander mcpyrate, which includes a more advanced version of imacropy.

[Technologicat]

This project is now obsolete.