SI-7292 Deprecate octal escape literals
SI-6899, prohibit dangerous, useless implicit conversions.

Increase eligibility requirements for implicit conversions,
such that T => U is ineligible if

  T <: Null    <or>   AnyRef <: U

This has the salutary effect of allowing us to ditch 16
ridiculous implicits from Predef, since they existed solely
to work around the absence of this restriction.

There was one tiny impact on actual source code (one line
in one file) shown here, necessitated because the literal null
is not eligible to be implicitly converted to A via <:<.

  def f[A](implicit ev: Null <:< A): A = null     // before
  def f[A](implicit ev: Null <:< A): A = ev(null) // after

As impositions go it's on the tame side.
Merge pull request #2625 from paulp/pr/no-useless-implicits

SI-6899, prohibit dangerous, useless implicit conversions.
Merge pull request #2342 from soc/SI-7292

SI-7292 Deprecate octal escape literals
SI-7292 Fixes test failures by updating *.check files

Looks like partest's confusion about / vs. \ was fixed between
the original Jenkins run of the fix for SI-7292 and its merge.
Merge pull request #2668 from soc/SI-7292-fix

SI-7292 Fixes test failures by updating *.check files