(GEOT-4963) Added fix for ContentFeatureStore.getCount() with startIndex...

Fix for ContentFeatureStore.getCount() with startIndex or MaxFeatures set (https://jira.codehaus.org/browse/GEOT-4963).
Modified test cases in ContentFeatureStore to test for getCount()
Added test cases to applicible extending classes. 
Yes, OSX should support the libraries, the JNI bindings are maintained by Justin, who's using them on OSX. The test does not run if it does not find the bindings though.