layer.conf: define ROSDISTRO within the meta-ros layer

Define a ROSDISTRO variable to record the current ROS distribution
code name for use within ROS-related recipes.
classes: locate packages in /opt/ros/${ROSDISTRO}

Following standard convention, place ROS/Catkin packages under the
prefix /opt/ros/${ROSDISTRO} (exported as ${ros_prefix}) rather than in
the usual ${prefix}.
README.md: update to reflect new ROS package prefix

Update the setup instructions to reflect the use of ${ros_prefix}.
ros-realtime-tests: updating to 0.1.3

This version fixes build problems with a ${prefix} other than /usr.
tf2-py: suppress rpath usage for Python extension libraries
Merge pull request #286 from housel/relocate-to-opt-ros-rosdistro

relocate ROS packages to /opt/ros/${ROSDISTRO} (resolves #214)
improving formatting after automated style check

After running oe-stylize.py on all recipes in recipes-ros, this
commit improves the formatting of some recipes.

To achieve this, I executed these commands in recipes-ros:
find . -name *.bb | sed 's#\(.*\)#./oe-stylize.py \1 > \1_sanitized#' | sh
find . -name *.bb | sed 's#\(.*\)#diff -Naur \1 \1_sanitized#' | sh > diffs

Then, I manually inspected the diffs file, and improved the
recipes.

For the DESCRIPTION line in the addressed recipes, the line width
of 100 characters was chosen, as the LIC_FILES_CHKSUM line and
SRC_URI line usually are also around about 100 characters long.
Hence, choosing a shorter line width, e.g. 80 characters, would
have only created more line breaks, but not reduced the need to
use a file viewer with which 100 characters line width can be
displayed. For the github file and diff viewer and most editors
on reasonably-sized screens, 100 character line width is no
problem.
check-patch-files.sh: initial commit

The check-patch-files script checks that all patch files in the
given directory are annotated with an 'Upstream-Status', and
that all patch files are at least noted in their top-level
directory (so we can assume they are used).

In case a violation is detected, it returns a non-zero exit code,
so that a travis-ci reports a violation as build failure.
.travis.yml: continuously check the patch files

This commit enables to use travis ci for continuous integration.
As bash is not a valid programming language setup for travis,
I simply used the default ruby environment, which also provides
a proper shell interpreter.
making layout indentation use 4 spaces

The description is not indented after line breaks. All other
information, i.e., the dependencies and SRCURI, are indented with
four spaces after line breaks. Shell scripts are indented with
multiples of four spaces.

In recipes-ros, I located and checked for tabulators and spacing
with these bash commands:

egrep '^ [^ ]+' . --exclude *.patch -R
egrep '^  [^ ]+' . --exclude *.patch -R
egrep '^   [^ ]+' . --exclude *.patch -R
egrep '^    [ ]+[^ ]+' . --exclude *.patch -R

While going through the recipes and manually improving the layout,
I also adjusted the descriptions to use maximal 100 characters
per line.
Merge pull request #288 from bulwahn/master-next

improving quality and quality assurance
addressing obvious flaw in commit 53796fc4

In commit 53796fc4, bitbake fails at parsing. It slipped through,
as I did not invoke any testing before submitting 53796fc4. This
commit resolves the obvious shortcoming.