Explain when buildlink3.mk files need to be included in other buildlink3.mk
files. Requested by rodent.
regen
GLPK 4.49 (release date: Apr 16, 2013)

        The new API routine glp_mincost_relax4, which is a driver to
        relaxation method of Bertsekas and Tseng (RELAX-IV), was added
        to the package. RELAX-IV is a code for solving minimum cost
        flow problems. On large instances it is 100-1000 times faster
        than the standard primal simplex method. Prof. Bertsekas, the
        author of the original RELAX-IV Fortran code, kindly permitted
        to include a C translation of his code in GLPK under GPLv3.

        A bug (wrong dual feasibility test) was fixed in API routine
        glp_warm_up. Thanks to David T. Price <dtprice@speakeasy.net>
        for bug report.

        Obsolete API routine lpx_check_kkt was replaced by new routine
        glp_check_kkt.

        IMPORTANT: All old API routines whose names begin with 'lpx_'
        were removed from API level and NO MORE AVAILABLE.
Changes 1.41.2:
* Update Vietnamese translation
* Update Croatian translation
* Update Brazilian Portuguese translation