Confusing auto-guessing of searched library

[ghost]

Presently, we'd decide that a library is searched if either 'name' or 'search' property is specified -- even if a bunch of sources is specified. So, if user mistakenly uses <search> instead of <library-path>, the libraries will all magically turn into searched, to much confusion.

I think the plan of attack is:

1. Deprecate <search> and use <library-path> instead, always.
2. Require that for target with sources, user explicitly say 'searched-lib', not just 'lib'. Or maybe even always require 'searched-lib', but that might be a backward-compatibility pain.