Separate the set of general projects from the Scala artifacts

This commit refactors the 2.11.x community file, by placing
into a common file all the projects that do not depend upon
the way in which the Scala artifacts and modules are generated.

By doing so, it becomes possible to test the same set of
projects using, for example, an optimized or non-optimized
compiler, or the GenBCode backend, or different Scala
options that should be used for all projects (to be specified
using using "vars.base").
Add community-2.11.x.sh: only this script will be called by Jenkins

By moving the dbuild version etc in this script, it becomes easier
to make changes without having to change the Jenkins configuration
every time.
Adding the community bootstrap file

The community bootstrap file performs a full bootstrap similar
to the traditional starr/locker/quick. Details to follow.
Bump scalacheck to 1.11.3
Cleanup and documentation of the bootstrap procedure

Now ready to go live.
Further updates to community-bootstrap
Added community-bootstrap-2.11.x.sh
Make shell scripts executable
Bump extraction version in "common" to 2.11.0-RC1
Place back set-version in starr-scala, just in case.
Merge branch 'master' of github.com:typesafehub/community-builds

Moved unforking to common-2.11.x.conf
Change in dbuild-runner, in order to allow "include" to find its files.

Since community and community-bootstrap now include common.conf,
it is necessary to launch dbuild without moving the working
directory.
Do not print the configuration on the console when starting
Disable set -x in dbuild-runner.sh
Allow for additional arguments (for instance, "-l" for local testing)
Use a simple env variable, rather than running egrep
Apply to community-bootstrap the "-P:continuations:enable" workaround
Merge pull request #17 from cunei/master

Adding bootstrapping config, and factoring out projects in a common file