io.readblock: now, we check that n1 and n2 are equal to the shape times bytes per elements of array to read.
If this is inconsitent, we do not use n1 but shape times bytes per elements instead. This allow to read files where the header is wrong because the number of bytes is larger than the max value of int32 header.
git-svn-id: https://svn.epfl.ch/svn/pnbody@66 f1771ac9-52fb-4361-9f77-cbfb7563c7d4