Require Java 1.6

This is a parent issue to track the work for requiring Java 1.6 in Sakai 2.9.

From the list:

DH:
2.8: recommend 1.6 - code compiles in 1.5
2.9: require 1.6 - no guarantee that code will compile/run in 1.5

AW:
If we want to drop 1.5 then we need to make sure that the
code compiles after adjusting Maven's compiler plugin
settings from 1.5 to 1.6. Last time I checked (early
December) the kernel failed to build due to an issue with
kernel util's validater.java due to "unmappable character
for encoding UTF-8 (53 cases)."

SS:
Yep lets get any required modifications committed into trunk, and enforce 1.6 as soon as possible so we can iron anything out early.

JFL:
Let's make this a 2.9 blocker and work on this at least as soon as 2.8.0 is released.