SI-6863 root cause fixed using factory of scala.runtime.*Ref

This commit does away with an error-prone division of labor between
UnCurry and LambdaLift, a division of labor by which UnCurry had to
anticipate under which circumstances LambdaLift creates a
scala.runtime.*Ref whose initial value is given by a an expression
including a Try in non-statement position. That sounds complicated,
and it is.

The solution so far (fixing SI-6863) is replaced by a simpler approach,
at the cost of forward binary comptability with pre-2.11 releases,
this time fixing the root cause of SI-6863.

From now on, a s.r.*Ref is instantiated via invocation of
a static factory method in the s.r.*Ref class in question.
Unlike the code that was emitted so far (which involved
NEW refclass, DUP, expr, INVOKESPECIAL refclass.<init>)
the "expr" doesn't appear on the operand stack on top
of the *Ref value being initialized. In other words,
the *Ref initialization is in statement position provided "expr" is.
indentation typo
Merge pull request #2462 from magarciaEPFL/backendish9

SI-6863 root cause fixed using factory of scala.runtime.*Ref