Do not depend on map ordering in tests.
Bump all Clojure 1.5.1 deps to 1.6.0.
Document :clean-non-project-classes and reword help output.

[ci skip]
Allow searching on multiple fields at once

Also allows searching by version.

Examples:

$ lein search "id:clojure group:org.clojure version:1.6"
$ lein search "id:postgres version:7.4"
$ lein search "id:postgres version:'7.4'"
run travis tests with oraclejdk8

for now, allow failure, since we're allowing failure for oraclejdk7

I see no indication that travis provides openjdk8, but I may be wrong
Merge pull request #1478 from MichaelBlume/use8

run travis tests with oraclejdk8
Add workaround for #1480.
Print error message when `upgrade` is unavailable.

Closes #1481.
Reword error message from `lein upgrade`.