Fix #5, compile issue due to generics craziness

When compiling at the command line, via mvn compile, compilation fails with the following error:
[ERROR] /Users/tobli/Development/jdbcmetrics/src/test/java/com/soulgalore/jdbcmetrics/driver/WhenDriverIsRegistered.java:[19,2] cannot find symbol
symbol  : method assertThat(java.util.List<java.sql.Driver>,org.hamcrest.Matcher<java.lang.Iterable<? super java.lang.Object>>)
location: class com.soulgalore.jdbcmetrics.driver.WhenDriverIsRegistered
This issue is noted in http://code.google.com/p/hamcrest/issues/detail?id=167
Work around by replacing Hamcrest matchers with for-loop.