library: Increase comm length to 64

For many years, the comm length has been set to 16. Previously to that
it was 8. This means for things like kworkers they all have very cryptic
names. The kernel is now going to increase this size to 64, so the
procps library will follow this length increase.

System tools may also increase their default length to 64, or keep it at
16; there is only so much screen real estate.

References:
 https://lkml.org/lkml/2018/5/17/16

proc/readproc.h

@@ -150,7 +150,7 @@ typedef struct proc_t {
     	egroup[P_G_SZ],	// status          effective group name
     	sgroup[P_G_SZ],	// status          saved group name
     	fgroup[P_G_SZ],	// status          filesystem group name
-    	cmd[16];	// stat,status     basename of executable file in call to exec(2)
+        cmd[64];	// stat,status     basename of executable file in call to exec(2)
     struct proc_t
 	*ring,		// n/a             thread group ring
 	*next;		// n/a             various library uses