These commits address a few minor issues in the Scala cross-version support in the build:

  1. Correct two missing `${scala.binary.version}` pom file substitutions.
  2. Don't update `scala.binary.version` in parent POM. This property is set through profiles.
  3. Update the source of the generated scaladocs in `docs/_plugins/copy_api_dirs.rb`.
  4. Factor common code out of `dev/change-version-to-*.sh` and add some validation. We also test `sed` to see if it's GNU sed and try `gsed` as an alternative if not. This prevents the script from running with a non-GNU sed.

This is my original work and I license this work to the Spark project under the Apache License.

Author: Michael Allman <michael@videoamp.com>

Closes #6832 from mallman/scala-versions and squashes the following commits:

cde2f17 [Michael Allman] Delete dev/change-version-to-*.sh, replacing them with single dev/change-scala-version.sh script that takes a version as argument
02296f2 [Michael Allman] Make the scala version change scripts cross-platform by restricting ourselves to POSIX sed syntax instead of looking for GNU sed
ad9b40a [Michael Allman] Factor change-scala-version.sh out of change-version-to-*.sh, adding command line argument validation and testing for GNU sed
bdd20bf [Michael Allman] Update source of scaladocs when changing Scala version
475088e [Michael Allman] Replace jackson-module-scala_2.10 with jackson-module-scala_${scala.binary.version}