converts Xt_xmap to an abstract datatype

src/Makefile.am

src/xt_ut_c.c

src/xt_xmap.c

src/xt_xmap.h

src/xt_xmap_all2all.c

src/xt_xmap_all2all.h

src/yaxt.h

tests/test_redist_p2p.c

tests/test_redist_p2p_parallel.c

tests/test_xmap.c

tests/test_xmap_parallel.c