add test to play with writing around the block boundaries
add test to play with writing around the block boundaries

refs #553

spthaolt/libsqlfs,guardianproject/libsqlfs,guardianproject/libsqlfs,spthaolt/libsqlfs,eighthave/libsqlfs,guardianproject/libsqlfs,spthaolt/libsqlfs,eighthave/libsqlfs,guardianproject/libsqlfs,eighthave/libsqlfs,spthaolt/libsqlfs,spthaolt/libsqlfs,eighthave/libsqlfs,guardianproject/libsqlfs,eighthave/libsqlfs