Regression - Unexpected string concatenation for selectors extending placeholders

[davidkpiano]

TEST:

%foo {
  test: outer;

  &-inner {
    test: inner;
  }
}

.foo {
  @extend %foo;

  &.inner { @extend %foo-inner; }
}

EXPECTED: (Ruby Sass and LibSass 3.2.5)

.foo {
  test: outer;
}

.foo.inner {
  test: inner;
}

ACTUAL: (with Node-Sass 3.4.x latest)

.foo {
  test: outer;
}

-inner.foo {
  test: inner;
}

[xzyfer]

Fixed by #1675. Creating a spec for good measure.

[xzyfer]

Spec added sass/sass-spec#596