Fix manifest and pure value warnings in common.
Add feature imports as needed in common.
Fix lift-markdown feature warnings.
Fix lift-json XML Elem constructor warnings.
Fix existential type warning in ScalaSig.

We still had code in place to support 2.8 that is no longer
needed, so we stop using existential types.
Fix a postfix operator warning in lift-json.
Fix inferred existential type warnings in lift-json.

There were a few places where the compiler was inferring
existential types when we needed to just be explicit about our
wildcard types.
Fix an erasure deprecation warning in lift-json.
Add a catch-all to JsonAST's Document match.

Document isn’t a sealed abstract class, so we need a wildcard
match at the end or we get a match exhaustiveness warning.
Feature imports to appease warnings in lift-json.

One in particular is due to a Scala compiler bug, but it’s been
annotated accordingly.
Fix an inferred existential type in lift-json.

Compiler quirkiness…
Implicit conversion->implicit class in lift-json.
Change fixme to explanation in Box.asA.

There was a FIXME about why existential types were being
used for Box.asA, but I figured it out, so I filled in the
reasoning as a comment.
Fix a catchall exception handler warning in actor.
Fix an implicit conversion feature warning.

Not sure what JsonCommand is for to begin with, but that’s
a separate question.
Import implicitConversions as needed in util.
Fix minimizeEmpty deprecations in util.

Elem has an extra required parameter in its constructor.
Import postfixOps as needed in lift-util.
Implicit conversions->implicit classes in util.
Drop some deprecated implicits to nuke warnings in util.