OSX build links dynamically against libusb

[skalarproduktraum]

The OSX Travis build links to libusb, resulting in

Unable to load native library: /private/var/folders/cl/j57y4y2504n1nnlyd4q41fj40000gp/T/vrpn-natives-tmp1381526963179001382/libjava_vrpn.dylib: dlopen(/private/var/folders/cl/j57y4y2504n1nnlyd4q41fj40000gp/T/vrpn-natives-tmp1381526963179001382/libjava_vrpn.dylib, 1): Library not loaded: /usr/local/opt/libusb/lib/libusb-1.0.0.dylib
  Referenced from: /private/var/folders/cl/j57y4y2504n1nnlyd4q41fj40000gp/T/vrpn-natives-tmp1381526963179001382/libjava_vrpn.dylib
  Reason: image not found
Did you include jvrpn-natives-mac in your dependencies?
[main] INFO VRPNTrackerInput - Initializing VRPN device DTrack at 10.1.2.201
/private/var/folders/cl/j57y4y2504n1nnlyd4q41fj40000gp/T/vrpn-natives-tmp1381526963179001382/libjava_vrpn.dylib: dlopen(/private/var/folders/cl/j57y4y2504n1nnlyd4q41fj40000gp/T/vrpn-natives-tmp1381526963179001382/libjava_vrpn.dylib, 1): Library not loaded: /usr/local/opt/libusb/lib/libusb-1.0.0.dylib
  Referenced from: /private/var/folders/cl/j57y4y2504n1nnlyd4q41fj40000gp/T/vrpn-natives-tmp1381526963179001382/libjava_vrpn.dylib
  Reason: image not found
Error initializing java_vrpn.
 -- Unable to find native library.
Error initializing remote device DTrack@10.1.2.201.
 -- Unable to find the right functions.  This may be a version problem.

java.lang.InstantiationException: vrpn.TrackerRemote.init(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Z

	at vrpn.VRPNDevice.<init>(VRPNDevice.java:61)
	at vrpn.TrackerRemote.<init>(TrackerRemote.java:80)
	at graphics.scenery.controls.VRPNTrackerInput.initializeTracker(VRPNTrackerInput.kt:62)
	at graphics.scenery.controls.VRPNTrackerInput.setTrackerAddress(VRPNTrackerInput.kt:32)
	at graphics.scenery.controls.VRPNTrackerInput.<init>(VRPNTrackerInput.kt:49)
	at graphics.scenery.controls.TrackedStereoGlasses.<init>(TrackedStereoGlasses.kt:24)
	at graphics.scenery.tests.examples.BileExample.init(BileExample.kt:33)
	at graphics.scenery.SceneryDefaultApplication.main(SceneryDefaultApplication.kt:123)
	at graphics.scenery.tests.examples.BileExample.main(BileExample.kt:99)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

on machines where it is not installed. The dependency should either be removed, or only statically linked.

This issue was migrated from scenerygraphics/scenery#73.