Fixes and improves travis ci build

Unfortunately since 3.0.1 one code coverage reporter segfaults (clang with autotools). I tried to fix it, but I'm not able to do so. Therefore I have disabled this configuration and added another one that only tests the build without code coverage. I also incorporated some other clean ups and most importantly I:

 changed `-std=c++11` to `-std=c++0x`

This seems to work with all gcc/clang versions and lowers the need for a modern gcc compiler massively. [Cpantesters](http://matrix.cpantesters.org/?dist=CSS-Sass%20v3.0.1) shows me successfull compilation and spec-test runs down to [gcc 4.4.3](http://www.cpantesters.org/cpan/report/c75a463b-6c03-1014-b41f-38e42d41344c). // CC @QuLogic 

If there are no objections I will merge this in tomorrow!

--

Also wanted to document some findings here I made with travis-ci to install certain packages:

```
  sudo add-apt-repository --yes ppa:ubuntu-toolchain-r/test
  wget -O - http://llvm.org/apt/llvm-snapshot.gpg.key | sudo apt-key add -
  sudo add-apt-repository --yes 'deb http://llvm.org/apt/precise/ llvm-toolchain-precise main'
  sudo add-apt-repository --yes 'deb http://archive.ubuntu.com/ubuntu/ lucid main restricted universe multiverse'
  sudo add-apt-repository --yes 'deb http://archive.ubuntu.com/ubuntu/ trusty main restricted universe multiverse'
  sudo add-apt-repository --yes 'deb http://archive.ubuntu.com/ubuntu/ trusty-security main restricted universe multiverse'
  sudo add-apt-repository --yes 'deb http://archive.ubuntu.com/ubuntu/ trusty-updates main restricted universe multiverse'
  sudo add-apt-repository --yes 'deb http://archive.ubuntu.com/ubuntu/ trusty-proposed main restricted universe multiverse'
  sudo add-apt-repository --yes 'deb http://archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse'

  sudo apt-get -qq update

  # sudo apt-get -qq install clang-3.5

  # sudo apt-get install -qq g++-4.2
  # sudo apt-get install -qq g++-4.4
  # sudo rm /usr/bin/cpp
  # sudo rm /usr/bin/gcc
  # sudo rm /usr/bin/c++
  # sudo rm /usr/bin/g++
  # sudo rm /usr/bin/gcov
  # sudo ln -s /usr/bin/cpp-4.4 /usr/bin/cpp
  # sudo ln -s /usr/bin/gcc-4.4 /usr/bin/gcc
  # sudo ln -s /usr/bin/c++-4.4 /usr/bin/c++
  # sudo ln -s /usr/bin/g++-4.4 /usr/bin/g++
  # sudo ln -s /usr/bin/gcov-4.4 /usr/bin/gcov

  # sudo apt-get -qq install llvm-gcc-4.2/lucid
  # sudo rm /usr/bin/gcov
  # sudo ln -s /usr/bin/llvm-gcov /usr/bin/gcov
```