FIX Merge more children PIDs to parents (fixes #72, maybe affects #14)

[allanlaal]

the algorithm was faulty and returned the command name too early for the old exe_only condition, which meant that it did not enjoy the merging up to parents that discriminate_by_pid had:

before:

    1.1 GiB +   1.9 MiB =   1.1 GiB	WebExtensions         
    5.2 GiB + 871.5 KiB =   5.2 GiB	Privileged Cont       
    6.6 GiB + 297.6 MiB =   6.9 GiB	firefox-esr (23)
    8.9 GiB +   1.1 GiB =  10.0 GiB	chrome (137)
   19.6 GiB + 321.8 MiB =  19.9 GiB	firefox (48)
   36.6 GiB +  13.1 MiB =  36.6 GiB	Isolated Web Co (30)  

after:

    6.6 GiB + 297.6 MiB =   6.9 GiB	firefox-esr (23)
    8.9 GiB +   1.0 GiB =  10.0 GiB	chrome (137)
   62.6 GiB + 338.8 MiB =  63.0 GiB	firefox (86)

[pixelb]

Looks good I think. Will check more later and merge. thanks!

[pixelb]

I'm not sure about the generality of this. Since it's now returning the exe rather than cmd, it's changing the following on my system:

- 23.1 MiB + 554.5 KiB =  23.6 MiB      firewalld
+ 23.1 MiB + 555.5 KiB =  23.6 MiB      python3.8 [updated]

Also if we're not restricting the parent grouping to the same exe, then might processes be incorrectly grouped in some cases (like being associated with systemd or other init processes)?