Handle manifest validation errors

[pingles]

Ensure blueshift handles manifests that fail validation errors. Should log the error and try again after the usual delay.

clojure.lang.ExceptionInfo: Invalid manifest. Check map for more details.
    at clojure.core$ex_info.invoke(core.clj:4403)
    at uswitch.blueshift.s3$validate.invoke(s3.clj:26)
    at uswitch.blueshift.s3.KeyWatcher$fn__8238$fn__8239.invoke(s3.clj:98)
    at uswitch.blueshift.s3.KeyWatcher$fn__8238.invoke(s3.clj:95)
    at clojure.core.async$thread_call$fn__5297$fn__5298.invoke(async.clj:390)
    at clojure.core.async$thread_call$fn__5297.invoke(async.clj:390)
    at clojure.lang.AFn.run(AFn.java:22)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

[pingles]

The validation fails with more information- would be good to include that in the error message too.