fixed message generation for local build

[LeroyR]

this fixes failing message generation in non catkin build folder.

Without this fix message_generation fails to generate message files if the given package folder is named differently than the pkg as the package of single files is guessed from the path which fails on non catkin workspaces which results in empty rosjava_message/pkg jars.

This fix forces all files in the given package parameter into the given pkg_name if only one argument is given for package-path and pkg-name.

[jubeira]

Hi @LeroyR, thanks for submitting this.
Could you provide more details about the use-case that was failing for you? What would be the correct way to test this?

[LeroyR]

Clone a message project into a random folder name (our jenkins) and build with cmake: mkdir build, cd build, cmake .., make
The package of each message definition is guessed from the path resulting in no code generation and empty jars