prototype for idle() in <unistd.h> (which i thought was against namespace
and sensibility guidelines, but...)
* consistently use xsignal() instead of signal(). we get known behaviour
in all cases (SA_RESTART), which is good for some borken foreign systems.
* remove signal.h from most files; it's unnecessary now
* fetch_url(): use `long chunksize' instead of ssize_t; it's more portable, and
we're setting chunksize with strtol() anyway
* xsignal(): only use SA_RESTART if it exists. SunOS 4.x doesn't have it
but has the inverse (SA_INTERRUPT). the original function i was inspired
from had this support (lib/signal.c, W. Richard Stevens' `UNP 2nd ed Vol 1').
* remove <termios.h> from util.c; it should be unnecessary now
70c01ac44a