bgq/cnk: double the size of the tracked segments array.


git-svn-id: svn://svn.valgrind.org/valgrind/branches/VALGRIND_3_8_BRANCH_BGQ@14285 a5019735-40e9-0310-863c-91ae7b9d1cf9
bgq/cnk: improve accuracy of the argc/v/envp/auxv initial image,
so that the XLC runtime doesn't crash at startup.


git-svn-id: svn://svn.valgrind.org/valgrind/branches/VALGRIND_3_8_BRANCH_BGQ@14286 a5019735-40e9-0310-863c-91ae7b9d1cf9