Bug#739697: src:dolfin: FTBFS on armhf and mips: virtual memory exhausted: Cannot allocate memory

[peter green]

I've been doing some tests on this interestingly it failed for me much 
earlier than on the buildd, maybe different systems give slightly 
different ammounts of usable address space or something. Anyway reducing 
optimisation levels etc doesn't seem to help, switching to 4.7 is 
looking more promising.

I'll follow up when i've done further tests.