Fix bug in C++ strel when calculating pad for image with more dimensions.
* src/strel.cc (post_pad, pre_pad): fix usage of "redim()" (which is an
accessor, not a modifer) by replacing it with "resize (n, 1)". This
caused a bug with random effect in imdilate and imerode when the SE had
less dimensions than the image.
* src/imerode.cc: add tests against this bug using imerode and imdilate.
Remove unecessary usage of %!shared blocks.
* nlfilter.m: remove FIXME about failing test due to bug in imdilate