[PATCH] support: Implement <support/descriptors.h> to track file descriptors

[Florian Weimer]

* Carlos O'Donell:

> On 12/1/18 6:25 AM, Florian Weimer wrote:
>> * Carlos O'Donell:
>> 
>>> On 11/29/18 11:43 PM, Florian Weimer wrote:
>>>> I could try to count more precisely how many bytes are actually needed,
>>>> but that seemed like a waste of mental resources.  Should I use
>>>> xasprintf instead, to make clear that there is no truncation?
>>>
>>> Yes, I think xasprintf solves all the problems.
>> 
>> Like this?
>> 
>> I also enhanced the test to test more conditions in the list merging
>> code.
>> 
>> Thanks,
>> Florian
>
> OK for master. Thank you!

I had to rename the local struct descriptor to struct procfs_descriptor,
due to a conflict with a mach header.  Pushed with that change.

Thanks,
Florian