isrow/iscolumn: add for dev Octave

also, cleans up my_isrow etc for supporting old Matlab 2008 (which
has no isrow/iscolumn for doubles/logicals)
add nnz command

Fixes #132.
fix logical indexing with a boolean sym

Fixes #131.
Merge pull request #133 from cbm755/isrow

add isrow/iscolumn, nnz, logical indexing w/ sym bool