Set scala pr validor on a tag

The code for multi-scala support doesn't work with the current uber-build
First cut at including zinc build in the uber-build.

* Add new operations `sbt-nightly`
* Add hooks to not build the ide itself.
* Instead of forking a git repo for zinc, just copy the local files.
* Use zinc's default scala versions.properties in lieu of the one from scala if doing a nightly.

Quick review from @skyluc and continued tweaking after this.
Fixes from @skyluc's comments
* Use checkAvailability correctly
* Do quick sanity check on zinc local build directory before copying.
* Always copy the build scripts from local zinc directory.
Now load sbt version from the .properties file.

* Eclipse will use the sbt version found in our properties file.
* The default in the config is used if we don't rebuild sbt.

Review by @skyluc
Add the ability to swap in/out the sbt properties file used in dbuild.

* Can swap the properties file used in dbuild
* Allows you to build IDE against different sbt version numbers
* Can use alternative branches of sbt/sbinary/sbt-republish from the default.
* Example nightly build for sbt 0.13.x (-SNAPSHOT).
Fix merge issues.

1) Always rebuilid zinc if it doesn't exist
2) Fix erroneous conditionals in BASH
3) Use new checkAvailability awesomeness from @skyluc.
Fiex from PR and bump to ide release script.

* Remove reference to old GIT URI for sbt dbuild scripts
* Fix logic for when to rebuild as well as using the always rebuild flag.
* Ensure IDE releases build necessary sbt projects :)
Fix issue where zinc URL is no logner need so check should be gone.
Fixes to zinc integration so the uber-build specifies the
sbt version deployed *and* the scala version used.

Review by @skyluc
Fixes from review and brokeness
Add missing sbt-launch.jar from gitignore.
Adds support to recreate a Scala versions.properties
Flags tweaks
Changes for 3.0.4v and new sbt build TO_SQUASH
Add sbt-tag info in properties file
Final changes 3.0.4 TO_SQUASH
Removes '-SNAPSHOT' in sbt full version for release
Bumps Scala IDE tag
(cherry picked from commit 133634e5e2653afa3b139b907d4a2cb74e7f6ed3)
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