Make ino_t a consistent size

[rm5248]

Proposed fix for #48

Effectively this just introduces a new type (pfs::pfs_ino_t) that is used instead of ino_t so that it is always the same size, no matter if ino_t is 32 bits or 64 bits.

This might break some current code due to the type changing and the size(number of bits) of the type changing.

I've done some minimal testing on my side

[dtrugman]

Thanks @rm5248, I will take a look at that in the following days!