util: Use posix_memalign for xmalloc_cacheline if available

A malloc library is expected to provide a better implementation
using the knowledge of its internal details.

ax_func_posix_memalign.m4 was obtained from:
http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_func_posix_memalign.m4

Acked-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
FAQ: Expand tabs

Acked-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Fix dot2pic make dependencies

I occasionally see the failure with "make -j32".

Acked-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>