Set glibc variables tracking the program name.

This also affects /proc/pid/cmdline.

I think another way to do this is Linux prctl and POSIX pthread_setname_np
(which on Linux wraps prctl). However, there are two problems: (1) prctl limits
the length to 16 characters including the NUL terminator and (2) not all
utilities read /proc/pid/comm (which prctl changes). It seems most utilities
prefer /proc/pid/cmdline which is based off of argv[0]. How it is actually
changed is not very clear. These glibc variables appear to affect it.

setproctitle (BSD, but also on Linux) is another way to change the title.
Merge pull request #434 from batrick/glibc-process-title

Set glibc variables tracking the program name.