Update maven compiler to 2.3.2

This change removes a redundant addition of source encoding and makes our
compiler match the current maven default. This amends the commit
4775b25a5932a2a24da2c55356936e2f98bff98c

Upstream issue http://jira.codehaus.org/browse/MCOMPILER-70
Merge remote-tracking branch 'upstream/master' into slow-hopper-world