[PATCH] 3 trivial test cases in o.a.g.c.mutable package

This patch contains 3 trivial test cases for the following classes
in the org.apache.geronimo.common.mutable package

1) MuShort - 90.1% clover coverage
2) MuInteger - 90.1% clover coverage
3) MuLong - 89.9% clover coverage