Print a message from configure if getpass() or crypt() were missing

if the system doesn't support getpass, we still default on the options
that require it which causes a build failure.  instead, only default
enable these when getpass is available.

if the system doesn't support crypt.h/crypt, then ENABLE_SVR_PASSWORD_AUTH
cannot work.  rather than default this to on all the time, do so only when
support for the header is found.

rather than doing ~ expansion

improbable, roughly 2**-1023
Regression in 0.49

Since the x.org rework, X has been installed into standard paths and not
its own random prefixes.  I think it's time we update the default paths
accordingly.

--HG--
branch : ecc

- comment on ecc binary size effects

--HG--
branch : ecc

--HG--
branch : ecc

--HG--
branch : keyondemand

Needs UI in server command line options

--HG--
branch : keyondemand

--HG--
branch : ecc

--HG--
branch : ecc

--HG--
branch : ecc

--HG--
branch : ecc

--HG--
branch : kexguess

--HG--
branch : ecc

Default for options.h shouldn't allow "none"

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>

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

--HG--
branch : insecure-nocrypto

--HG--
branch : insecure-nocrypto

--HG--
branch : sha2

  getting keyed incorrectly

--HG--
branch : sha2