Change BackupStorage to use xmemalign
Change BackupStorage to use xmemalign

Using xmemalign is more concice, and it provides better error message. I
discovered this when I tried running with a non-power-of-two segment
size and my backup quit from a bad_alloc exception.

Frank-Wu/RamCloud,matrix207/RAMCloud,jcarreira/ramcloud,rstutsman/RAMCloud,utah-scs/RAMCloud,anirajk/RAMCloud,utah-scs/RAMCloud,utah-scs/RAMCloud,jblomer/ramcloud,taschik/ramcloud-load-manager,taschik/ramcloud-load-manager,jblomer/ramcloud,DavidLi2010/ramcloud,jblomer/ramcloud,IMCG/RamCloud,Frank-Wu/RamCloud,QingkaiLu/RAMCloud,jcarreira/ramcloud,SMatsushi/RAMCloud,IMCG/RamCloud,anirajk/RAMCloud,IMCG/RamCloud,IMCG/RamCloud,SMatsushi/RAMCloud,taschik/ramcloud-load-manager,Frank-Wu/RamCloud,QingkaiLu/RAMCloud,alexandermerritt/ramcloud,taschik/ramcloud-load-manager,taschik/ramcloud,mrdiegoa/ramcloud,rstutsman/RAMCloud,matrix207/RAMCloud,QingkaiLu/RAMCloud,jblomer/ramcloud,y-higuchi/ramcloud,QingkaiLu/RAMCloud,anirajk/RAMCloud,y-higuchi/ramcloud,jblomer/ramcloud,Frank-Wu/RamCloud,utah-scs/RAMCloud,taschik/ramcloud,y-higuchi/ramcloud,mrdiegoa/ramcloud,behnamm/cs244b_project,anirajk/RAMCloud,Frank-Wu/RamCloud,DavidLi2010/ramcloud,taschik/ramcloud,taschik/ramcloud,IMCG/RamCloud,matrix207/RAMCloud,QingkaiLu/RAMCloud,DavidLi2010/ramcloud,Frank-Wu/RamCloud,behnamm/cs244b_project,SMatsushi/RAMCloud,matrix207/RAMCloud,QingkaiLu/RAMCloud,utah-scs/RAMCloud,matrix207/RAMCloud,SMatsushi/RAMCloud,anirajk/RAMCloud,y-higuchi/ramcloud,jcarreira/ramcloud,anirajk/RAMCloud,matrix207/RAMCloud,DavidLi2010/ramcloud,jcarreira/ramcloud,y-higuchi/ramcloud,behnamm/cs244b_project,alexandermerritt/ramcloud,rstutsman/RAMCloud,DavidLi2010/ramcloud,alexandermerritt/ramcloud,jcarreira/ramcloud,SMatsushi/RAMCloud,rstutsman/RAMCloud,rstutsman/RAMCloud,mrdiegoa/ramcloud,alexandermerritt/ramcloud,mrdiegoa/ramcloud,behnamm/cs244b_project,SMatsushi/RAMCloud,behnamm/cs244b_project,alexandermerritt/ramcloud,alexandermerritt/ramcloud,DavidLi2010/ramcloud,mrdiegoa/ramcloud,jblomer/ramcloud,mrdiegoa/ramcloud,utah-scs/RAMCloud,taschik/ramcloud,taschik/ramcloud-load-manager,behnamm/cs244b_project,y-higuchi/ramcloud,rstutsman/RAMCloud,jcarreira/ramcloud,IMCG/RamCloud