Fix for newer SO-DIMM / external memory.
See http://www.xilinx.com/support/answers/44814.htm
Fixed bug:
- merge algorithm was only able to merge a number of blocks which was of the form 2**n
- merge algorithm is now able to merge an array of arbitrary size.

Example:
Before:  sort_demo 0 1 2 # did work
         sort_demo 0 1 3 # didn't work!!!

Now:     sort_demo 0 1 3 # does work now!
Merge pull request #1 from sebastianmeisner/master

Fix for newer SO-DIMM / external memory.