sysconf is not. This causes glib to try and malloc UINT_MAX bytes of memeory
which basically translates to -1 bytes. Sanity check the value returned by
sysconf (_SC_GETPW_R_SIZE_MAX) to see that it's really implemented. This
fixes an abort people started to see in Glib-based applications.
Reported by: Shin-ichi YOSHIMOTO <yosimoto@waishi.jp>
