Refactor clang::tarball recipe

 * Renounce to dynamically construct download URL.
   The download link is now defined as a cookbook attribute, since
   llvm.org packages do not follow stable naming conventions.
 * Use 'ark' resource to download and install clang tarball.
[clang 3.1+] Don't symlink to removed 'llvm-ld'

From http://llvm.org/releases/3.1/docs/ReleaseNotes.html:

> The llvm-ld tool has been removed. The clang driver provides a
> more reliable solution for turning a set of bitcode files into a
> binary. To merge bitcode files llvm-link can be used instead.

**KISS Note:**

This cookbook is not (yet) oriented to install "all possible" clang versions.
If wanting to do so, the list of binaries to symlink should be
dynamically constructed based on clang version, or extracted as cookbook
attribute to give more flexibility.
Bump clang version to 3.3
Update sbt-extras cookbook

Most Important Changes:
* almost ready to integrate with official paulp/sbt-extras
* sbt 0.13.0 is now default launcher
* better pre-installation of sbt and scala boot libraries
* verbose mode enabled to better show which sbt and scala versions are used during the build
* custom JVM options simplified, since sbt-extras now include some of our tweaks.
Revamp 'postgresql': multi-versions and PostGIS

- Use PDPG apt repository
- Install multiple instances (9.1, 9.2 and 9.3)
- Preinstall PostGIS 2.1 for all instances
- Only supports Ubuntu 12.04LTS (all outdated and unused recipes
  original Opscode cookbook have been removed. e.g. Redhat/RPM flavors)
- Customize /etc/init.d/postgresql to be backward compatible (default
  postgresql version is used if not specified), and to prevent to start
  more than one instance at the same time
- Database copy to RAMFS storage is now explicitly handled by chef provision
  (instead of idempotent copy in /etc/init.d/postgresql script)
- CI-Specific tunings are still there (and parametrized, if not already)
  see original commits 29f200f5bc and f34cf19a68.
- Clean and fix handling of /etc/sysctl.conf and /etc/sysctl.d/...
- Refactor 'sysctl' cookbook to dynamically compute System V shared
  memory depending on 'postgresql' configuration (`max_connection`)
- Add a parameter in 'ramfs' cookbook to adjust disk size (default is
  still 512M)
- Set max_connections = 255 as default (No more needed to override this
  attribute in travis-images standard template)

The resulting cookbook is simply organized (less recipes) and strictly
focused on Continuation Integration context.
The relashionship with very old forked version (0.11) of original Opscode
cookook doesn't make sense any more. For these reasons I bump this
cookbook to version 2.0.0, in order to clearly mark this step, but not
to express maturity level.
[postgresql] Fix bug in RAMFS management

In order to keep it simple, data for all instances are always copied.
We could try to improve this to spare some RAMFS space, but it is
quite more tricky to manage the different use cases in a robust manner.
Update RVM to 1.22
Merge pull request #222 from travis-ci/hh-update-rvm

Update RVM to 1.22
Merge pull request #220 from gildegoma/update-sbt

Major updates in sbt-extras cookbook
Merge pull request #221 from gildegoma/multi-pg-and-postgis

Revamp 'postgresql': Add support of PostgreSQL 9.2 and 9.3, and also PostGIS 2.1
don't install rubygems-bundler gem
Update default to the latest version
Merge pull request #223 from davglass/nodejs

Update default to the latest version
Upgrade elasticsearch to v0.90.5

Version 0.90.5 of elasticsearch is the latest stable version
Merge pull request #224 from clintongormley/patch-1

Upgrade elasticsearch to v0.90.5
Allow setting custom host names for the worker config.

Relevant for upcoming caching services.
Fix erb template.
Add configuration for S3 cache details.
Timousse.
"Booleanify" relevant postgresql attributes

Note that it is hopefully not required to convert ruby boolean values as 'on' / 'off' in templates,
since "Boolean values can be written as on, off, true, false, yes, no, 1, 0 (all case-insensitive)"
See http://www.postgresql.org/docs/9.3/static/config-setting.html#CONFIG-SETTING-NAMES-VALUES