[pycaffe] net spec layers can have ntop=0
[pycaffe] net spec layers can have ntop=0

In this case, the Function is returned instead of a Top, which can be
assigned a name if desired.

Thanks @philkr for an earlier implementation of this.

wangg12/caffe,CZCV/s-dilation-caffe,gnina/gnina,longjon/caffe,wangg12/caffe,tackgeun/caffe,tackgeun/caffe,CZCV/s-dilation-caffe,longjon/caffe,tackgeun/caffe,gnina/gnina,gnina/gnina,gnina/gnina,longjon/caffe,wangg12/caffe,longjon/caffe,tackgeun/caffe,gnina/gnina,CZCV/s-dilation-caffe,gnina/gnina,CZCV/s-dilation-caffe,wangg12/caffe