pid). We have to be careful to choose() either strtol() or strtoul()
depending on whether the string appears to be signed or unsigned.
Always using strtoul() is unsafe on 64-bit platforms since the
uid might be represented as a negative number and (unsigned long)-1
on a 64-bit system is 0xffffffffffffffff not 0xffffffff.
Fixes a problem with uids larger than 0x7fffffff on 32-bit platforms.