Suggestion: use getpagesize()

[Sierra-Sam]

patchelf.cc has hard-coded values for pageSize.
I believe it would be more portable if PageSize were
discovered using the getpagesize() function.

Also, when I do code that involves size of any kind,
including page size, I use type, size_t. But, in this
case no one would care. Besides, getpagesize()
returns an int, but that is only because it is old.

[darealshinji]

I guess this can be closed because of 35ecfa7

[fsateler]

Even more now that #73 has been merged.