Mantid reading multiperiod nexus and multiperiod data with SANS GUI

[NickDraper]

We discovered a number a errors last night on SANS2D.

Reading a multiperiod nexus file results in an incorrect grouping of the workspaces. (raw file reading is fine) 
This is and example 

loadnexus(".....SANS2D00005508.nxs","w5508") 

the file contains 13 periods, results in 

    w5508 
       |-w5508_2 
       |-w5508_3 
       |-w5508_4 
       |-w5508_5 
       |-w5508_6 
       |-w5508_7 
       |-w5508_8 
       |-w5508_9 
       |-w5508_10 
       |-w5508_11 
       |-w5508_12 
       |-w5508_13 

    w5508_1

More importantly for SANS2D the SANS gui cannot deal with multi-period data. (this is undoubtedly because it has not been tested as no files have existed)

There are two problems. 
On windows the files are to big for a 4GB system and everything falls over -??
On the Linux box it is happier but produces log file reading faults. - ??

SANS2d runs 5511 to 5519 should contain multi period data 

[NickDraper]

This issue was originally trac ticket 1285