Clarify a few points of documentation. Fixes #1475.

[ci skip]
Use dep-key for distinct call in pom task.

group/artifact version tuple isn't enough to de-dupe correctly.

Fixes #1494.
Emit success message after install.

Normally I prefer to remain silent if everything succeeds, but the
fact that install calls pom and jar, which are not silent, means it's
confusing if you don't see anything for install itself.
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' of github.com:CraZySacX/leiningen