Increase compile performance

Based on [1], a simple trick that seems to reduce total build time, especially for multimodule projects.

Here follows what I could experiment on my machine (GNU / Linux 64bit / OpenJDK 6)

BEFORE

[INFO] Apache Syncope Root ............................... SUCCESS [0.140s]
[INFO] Apache Syncope Quality ............................ SUCCESS [1.742s]
[INFO] Apache Syncope .................................... SUCCESS [2.338s]
[INFO] Apache Syncope Build Tools ........................ SUCCESS [6.164s]
[INFO] Apache Syncope Client ............................. SUCCESS [4.062s]
[INFO] Apache Syncope Core ............................... SUCCESS [2:00.219s]
[INFO] Apache Syncope Console ............................ SUCCESS [10.799s]
[INFO] Apache Syncope Archetype .......................... SUCCESS [1.828s]
[INFO] Apache Syncope Hibernate enhancer ................. SUCCESS [1.076s]
[INFO] ----------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2:29.002s
[INFO] Finished at: Mon Apr 30 08:51:18 CEST 2012
[INFO] Final Memory: 97M/594M
[INFO] ------------------------------------------------------------------------

AFTER

[INFO] Apache Syncope Root ............................... SUCCESS [0.142s]
[INFO] Apache Syncope Quality ............................ SUCCESS [1.593s]
[INFO] Apache Syncope .................................... SUCCESS [2.134s]
[INFO] Apache Syncope Build Tools ........................ SUCCESS [5.953s]
[INFO] Apache Syncope Client ............................. SUCCESS [3.510s]
[INFO] Apache Syncope Core ............................... SUCCESS [1:54.870s]
[INFO] Apache Syncope Console ............................ SUCCESS [7.745s]
[INFO] Apache Syncope Archetype .......................... SUCCESS [1.916s]
[INFO] Apache Syncope Hibernate enhancer ................. SUCCESS [0.633s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2:19.145s
[INFO] Finished at: Mon Apr 30 08:58:10 CEST 2012
[INFO] Final Memory: 61M/594M
[INFO] ------------------------------------------------------------------------

I'ts only 10 secs, but why not?

[1]https://gist.github.com/2508909