design question: mvn support seems to be complicated

[lispnik]

From some debugging in #706 the mvn/aether code attempts to use already installed Maven and depending on its version, call different things.

I don't think ABCL should do that.

The mvn support in ABCL should bootstrap itself with a specific version of Maven and just use that rather than whatever is going on in $M2_HOME etc. This seems to be what tools such as leiningen do (via pomegranate – a wrapper for eclipse/maven aerther).

Thoughts on improving the ABCL maven support by bootstrapping with a specific version included?

[fosskers]

See also #704 .