Speed up dev tools parsing by optimizing checking for cells in multidime...

...nsional arrays.

Latency of 
http://localhost/graph_page_data.php?test=140530_NC_2Z3 on my workstation (from chrome dev timeline, main request only): -14.4%, -1.1s:
before mean 7.964s:
8.19s
7.85s
7.93s
7.94s
7.91s
after mean 6.816s:
6.83s
6.72s
6.80s
6.93s
6.80s