+ Build System
+ * Require g++ v4.7 at least to not speak prehistorical C++.
+ * Require Boost 1.48 (for signal2 component).
+ * Tracing is now always enabled (no way to turn it out)
+ * Move headers around to sort them out on installed systems:
+ - instr/instr.h -> simgrid/instr.h
+ - instr/jedule/* -> simgrid/jedule
+ - simdag/datatypes.h was removed
+ - simdag/simdag.h -> simgrid/simdag.h
+ - msg/datatypes.h was removed
+ - msg/msg.h -> simgrid/msg.h
+