We now use boost::icl::interval_set internally, consuming extremely
lower amounts of memory. boost::icl was introduced with Boost 1.46;
Debian 7.0 comes with 1.49, so this dependency should be no problem
anymore.
Both the class interface and the memory-map file format stay the same.
Change-Id: I38e8148384c90aa493984d0f6280817df00f1702
