Some changes added to compile and run with Java 6 and Java 7.

  - correction of errors with Javac 6:
    - fields accessibility of type variable (jls 4.4).

Change-Id: I202b8767e9d4c6642e1e15e9a0570de764db0b4c
Signed-off-by: Jerome Pilliet <pilliet@univ-mlv.fr>