> I have one question regarding the version numbers:
> How can I check in my code (at compile time) which pluginlib version is available and conditionally use the new functionality?

It looks like that this is not yet possible or have I missed something obvious?

The CMake macro "rosbuild_make_distribution" does nothing and the pluginlib does not specific any version number in C++ code.
Using the ROS version is no alternative since
a) a program does not (necessarily) depend on roscpp and
b) both packages (roscpp and pluginlib) does not need to be updated at the same time - so the ROS version is not related to the pluginlib version.

Since many parts of ROS are currently refactored into separately usable libraries I would propose that each of them should specify the version number in a form that makes it available for compile time 
conditional checks.

Dirk