Fix system cmd memleak

[catfact]

due to a subtlety of the pthreads API, the worker threads created in system_cmd.c were leaking all the memory of the child processes they spawned.

(the child process in latest version being a big ol' find that ate up a rather shocking 10MB a pop with a goodly number of scripts installed. [um, actually that's not quite right. it's mapped but unwired, or something.])

detaching the thread fixes this, it seems.

also uncrustified that file, because someone has their vim set on 2space again. :)

[catfact]

last commit is a bit silly, but it reduces mem usage of the subcommand by about 25% compared to find (AFAICT), and is probably faster

[tehn]

thank you for spotting this. i clearly need to learn more about pthread.

[tehn]

@catfact i suspect this is the problem:

norns/matron/src/system_cmd.c

Line 17 in 71f2c1e

#define CMD_BUFFER 8192

for super super long folder listings perhaps it's just running out of memory and plowing over

[catfact]

oh, ha. indeed.

i'll do another round of cleanup on this. strcat is basically pure evil...

[tehn]

oy oy oy i apologize