SI-8197 Only consider immediate params for defaults, overloading

A recent commit fixed the behaviour of overloading with regards
to discarding candiates that include default arguments. The old
check was checking the wrong flag.

But, the new code is actually checking all parameter lists for
defaults, which led to a regression in scala-io, which is distilled
in the enclosed test case. Applications are typechecked one
parameter list at a time, so a holistic check for defaults doesn't
seem to make sense; only defaults in the first parameter list
ought to count.
SI-8324 Fix regression in override checks for sealed classes

adeffda25 changed `Symbol#isEffectivelyFinal` to help the optimizer
by inferring finality within sealed class hierarchies.

However, this change wasn't neccesarily welcome for other clients of
that method. In the enclosed test case, we see that overriding checks
in `RefChecks` regressed.

This commit moves the enhanced version into a new method and
selectively uses it in the optimizer (and the tail call optimizer).
Fix ./build/<stage>/bin/scaladoc

Was:

    ./build/quick/bin/scaladoc -version
    Exception in thread "main" java.lang.NoClassDefFoundError: scala/tools/nsc/ScalaDoc
    Caused by: java.lang.ClassNotFoundException: scala.tools.nsc.ScalaDoc

Now:

    % for tool in ./build/quick/bin/{fsc,scala,scalac,scaladoc,scalap}; do $tool -version; done
    Fast Scala compiler version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scala code runner version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scala compiler version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scaladoc version 2.11.0-20140222-144307-b0dcf79875 -- Copyright 2002-2013, LAMP/EPFL
    Scala classfile decoder version 2.0.1 -- (c) 2002-2013 LAMP/EPFL
Merge pull request #3572 from retronym/ticket/8197

SI-8197 Only consider immediate params for defaults, overloading
Merge pull request #3573 from retronym/ticket/8324

SI-8324 Fix regression in override checks for sealed classes
Merge pull request #3575 from retronym/ticket/scaladoc-qbin

Fix ./build/<stage>/bin/scaladoc