Code review comment for lp://staging/~niemeyer/juju-core/func-validators

Reviewers: mp+157924_code.launchpad.net,

Message:
Please take a look.

Description:
charm: use functions for validation

https://code.launchpad.net/~niemeyer/juju-core/func-validators/+merge/157924

(do not edit description out of merge proposal)

Please review this at https://codereview.appspot.com/8585043/

Affected files:
   A [revision details]
   M charm/url.go
   M charm/url_test.go
   M cmd/juju/bootstrap.go