Linux 3.10

@yshui's 3.10 compatibility patches worked, but a few of them addressed the Linux kernel's move to make `struct proc_dir_entry` a private interface by duplicating the definition. @behlendorf pointed out that is prone to break, so I wrote a patch to implement his suggestion to "rework the __kstat_install/__kstat_delete handlers to only pass around the opaque handle". I also fixed the merge conflict in one of yshui's other patches that replacing his proc_dir_entry patches caused.

This is complemented by zfsonlinux/zfs#1494. It contains an autotools check that is slightly better than the one @yshui proposed in zfsonlinux/zfs#1458.