Aggressive resolve policy for lein.change functions
Disable problematic but non-essential test

Failure must have something to do with namespace state that
changes between running tests in REPL and running the full suite.

Test is not an important property, so just commenting out.
Use existing helper instead

1. Reorganise tests a bit so loading property still checked.
2. Add explicit exception if unexpected type to `collapse-function`
3. Unrelated addition of test to show leading `:` ignored in nested paths
Merge pull request #1531 from crisptrutski/load-function-via-cli

Ensure supporting namespace is loaded when passing custom function to `lein change`