Imho

I have come across it used with this sort of meaning in simialr contexts — though I confess I can't really see why this would be relevant here?!

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Note added at 1 day17 hrs (2012-12-23 22:17:09 GMT)
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Ah, your other question that I've just seen gives vital extra context explaining the use of 'outil' here, in the light of which, I don't think my answer holds up here.

French term (edited): bien outillé

That's what I think this means... The primitives may be well written, well documented, well tested... but they are known to work well.

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Note added at 1 day22 hrs (2012-12-24 03:45:47 GMT)
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Some references:

robust
(adj.) When used to describe software or computer systems, robust can describe one or more of several qualities:
a system that does not break down easily or is not wholly affected by a single application failure
a system that either recovers quickly from or holds up well under exceptional circumstances
a system that is not wholly affected by a bug in one aspect of it
http://www.webopedia.com/TERM/R/robust.html

The word robust, when used with regard to computer software, refers to an operating system or other program that performs well not only under ordinary conditions but also under unusual conditions that stress its designers' assumptions.
[...]
Robustness is something that should be designed into software from the ground up; it is not something that can be successfully tacked on at a later date.
http://www.linfo.org/robust.html

Robust Software Systems
Professor Emery Berger
Department of Computer Science
University of Massachusetts
In this seminar, we'll examine systems-based approaches to making robust software that performs well regardless of workload, architecture, or data access patterns.
http://people.cs.umass.edu/~emery/classes/CMPSCI691P-Fall200...

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Note added at 4 days (2012-12-26 17:18:00 GMT)
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Another aspect of "robust" that may apply here:

robust
(adj.) When used to describe software or computer systems, robust can describe one or more of several qualities:
[...]
a system that comes with a wide range of capabilities. (It should be noted that this last sense of the term robust is not uniformly accepted in technical circles. The term is typically used in this sense in the marketing of software or computer systems to emphasize a selling point and does not refer to the first three meanings of the term.)
http://www.webopedia.com/TERM/R/robust.html

Originally, I left off this part of the webopedia definition because of the parenthetical caution, but the more I think about it, the more I think this aspect of "robustness" may pertain in the French text,

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Note added at 5 days (2012-12-28 02:16:58 GMT)
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I just came across this paper written by prof at the California Institute of Technology...
"Robust Control Theory and Applications
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA337888