diff_drive: use wheel separation and radius multipliers for the odometry
diff_drive: change the limiter policy to open-loop

Also prevent a potential problem with uninitialized command structure
diff_drive: fix nasty crash on some platforms (OSX)

This one is nasty. Because we _manually_ load the controller at runtime,
we have to build it with special flags to export the run-time type
information (rtti) needed for stuff like dynamic_cast. But we don't, and
here it's simpler to just use a static_cast.

See here: http://gcc.gnu.org/faq.html#dso

A dynamic_cast without a check is stupid anyway. (_what could possibly
go wrong?..._)
diff_drive: fix dependencies

Too few in CMakeLists.txt, too many in package.xml
Merge pull request #25 from po1/fix-missing-rtti

diff_drive: fix nasty crash on some platforms (at least on OSX)
Merge pull request #24 from po1/fix-depends

diff_drive: fix dependencies
diff_drive: add unit test for parameter multipliers
Merge pull request #23 from po1/open-loop-limiter

Change the limiter policy to open-loop in the diff-drive controller
Merge pull request #22 from po1/odom-multipliers

Take diff drive parameter multipliers into account in the odometry
Merge branch 'hydro-devel' into cmd-vel-timeout

Conflicts:
	diff_drive_controller/CMakeLists.txt
	diff_drive_controller/src/diff_drive_controller.cpp