JDK level compilation switched to 7
JDK level compilation switched to 7

Since commit ea5e38c17986be0786389111a4b8d9b99350c0a2, JDK 7 is used
for compilation.
Some class (Files, Path, ...) are now used and require JDK 7.
This change is mainly to link a JDK 7 when Eclipse m2e is used (6 used
before, so compilation problem, manual update required).

This fixes #27

codehaus-plexus/plexus-utils,codehaus-plexus/plexus-utils,codehaus-plexus/plexus-utils