The UseUse::$alias node can now be null if an alias is not
explicitly given. As such "use Foo\Bar" and "use Foo\Bar as Bar"
are now represented differently.
The UseUse->getAlias() method replicates the previous semantics,
by returning "Bar" in both cases.
The parser will now always generate Identifier nodes (for
non-namespaced identifiers). This obsoletes the useIdentifierNodes
parser option.
Node constructors still accepts strings and will implicitly create
an Identifier wrapper. Identifier implement __toString(), so that
outside of strict-mode many things continue to work without changes.
It's likely that an error after -> will trigger another one due to
missing semicolon without shifting a single token. We prevent an
immediate failure in this case by manually setting errorState to 2,
which will suppress the duplicate error message, but allow error
recovery.
A Nop statement will be inserted into statement lists if there are
any trailing comments in the list (which would otherwise not be
associated with any node).
The pretty printer output currently still contains a superfluous
newline.
