[Beignet] silently does nothing on large arrays (was ICD interface (only) broken on Haswell)

[Rebecca N. Palmer]

Control: retitle -1 beignet: silently does nothing on large arrays
(previous discussion: 
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=781875 )

This isn't a Haswell-specific problem (and might not be ICD-specific 
either: did you test that at these sizes, or only with the testsuite?), 
it's a large-array-specific problem: I simply hadn't tried arrays that 
big before.

The array size required to trigger it decreases as the number of arrays 
(arguments to the kernel being run, not total existing) increases, 
suggesting a total-memory limit: on my system, approximately 
2x240Mifloat, 3x160Mifloat, or 5x100Mifloat, but these vary ~10% from 
run to run.  (Hence, re-adding the per-array size limit probably 
wouldn't completely avoid the problem, though I haven't actually tried 
that.)

These sizes do _not_ appear to depend on free system memory, but due to 
their variability and the limited range I can test before running into 
"running out of memory in beignet hangs the entire system" 
(https://bugs.launchpad.net/ubuntu/+source/beignet/+bug/1354086 ), I 
cannot be completely sure of this.
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