Fix remaining CI issues

[bilderbuchi]

The new CI build has a couple of remaining TODOs/problems, I'll try to deal with those in further PRs

• Linux build sometimes fails with " "g++-4.9: internal compiler error: Killed (program cc1plus)"", due to lack of RAM/swap, apparently. (also happens on Arturo's build). Could be that this or this could reduce g++ memory consumption.
• Sometimes (currently often) the apt-get step in linux builds fails with Error 137 when installing g++-4.9, reason currently unknown.
• doc builds fail, see weird failures on OF Travis HalfdanJ/ofDocGenerator#3. set to allow failure for now.
• Move docs to docker builds (all packages are whitelisted), cf. How to check if packages were installed successfully in a container build? travis-ci/travis-ci#4557
• Confirm cache works correctly, maybe have to remove ever-changing files (.awk?)
• add allAddonExample to build stage
  • Ask for 14.04 beta access (done but doesn't work when using macos builds, too) Done - needs a dist: trusty and sudo: required (so does not work on the docker builds)
  • dist: trusty flag to activate 14.04 workers does collide with os: osx, making those builds run on Linux. Therefore, this has been postponed until this is fixed by travis.
  • With 14.04, we (hopefully) get recent enough versions of the addons' dependencies (e.g. opencv, assimp) to activate compiling the allAddonsExample, which would cover more of the OF codebase.

[bilderbuchi]

so, g++ and apt-get being killed seems to have disappeared now.
I have no idea how to fix the docs build.

[danoli3]

@arturoc Want to just add Linux to Allowed Failures for the moment till that is sorted?

[arturoc]

it's now fixed

[HalfdanJ]

Regarding the doc generator. Please just remove it form the travis file for now. I'm working on an update, but there is no reason for now to letting it fail all the time

[bilderbuchi]

@HalfdanJ I just did, looks godd so far.