Name threads in the programs

[pieterlexis]

Short description

This PR adds names to our progam's threads. These show up in ps -eT and in certain htop configuration. They might help users (and us) to figure out where the bottleneck in an application exists.

Closes #6974

Tested on

• Linux
• FreeBSD
• Mac/Darwin
• NetBSD
• OpenBSD

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[pieterlexis]

Reading the diff, I think a threadname.hh with a setThreadname function would help :)

[chbruyand]

By curiosity, why do you remove constness of the name argument everywhere ?

[rgacogne]

Note that the _np suffix stands for non-portable, so we should probably check that the function is available during configure.

[zeha]

Note that on BSDs, the function has a different signature:

/usr/include/pthread.h:int	pthread_setname_np(const char*);

[Habbie]

Note that on BSDs, the function has a different signature:

Actually that's the Darwin signature.. the BSDs have at least two other signatures. @pieterlexis has it under control!