in the random generation input

Changes this from a compile-time switch to a command-line option.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>

Update URLs with https

Try to read from /dev/urandom multiple times, take input from extra sources,
and use /dev/random when generating private keys

if that wasn't what the client requested.

if public key authentication is disabled

- Fix build if ENABLE_SVR_REMOTETCPFWD is disabled but ENABLE_SVR_LOCALTCPFWD
  is enabled

specific IPv6 addresses.

From OpenWRT,
https://dev.openwrt.org/browser/trunk/package/dropbear/patches/300-ipv6_addr_port_split.patch

Got rid of ENABLE_AGENTFWD macro.

It makes it a bit more obvious why there's a test there since HAVE_FORK
is the normal case.

If we build out of tree and then run `make clean`, we hit an
infinite loop where libtommath tries to enter subdirs that don't
exist and run `make clean`.