options: Complete the transition to numeric toggles (`#if')

For the sake of review, this commit alters only the code; the affiliated
comments within the source files also need to be updated, but doing so
now would obscure the operational changes that have been made here.

* All on/off options have been switched to the numeric `#if' variant;
  that is the only way to make this `default_options.h.in' thing work
  in a reasonable manner.

* There is now some very minor compile-time checking of the user's
  choice of options.

* NO_FAST_EXPTMOD doesn't seem to be used, so it has been removed.

* ENABLE_USER_ALGO_LIST was supposed to be renamed DROPBEAR_USER_ALGO_LIST,
  and this commit completes that work.

* DROPBEAR_FUZZ seems to be a relatively new, as-yet undocumented option,
  which was added by the following commit:

    commit 6e0b539e9ca0b5628c6c5a3d118ad6a2e79e8039
    Author: Matt Johnston <matt@ucc.asn.au>
    Date:   Tue May 23 22:29:21 2017 +0800

        split out checkpubkey_line() separately

  It has now been added to `sysoptions.h' and defined as `0' by default.

* The configuration option `DROPBEAR_PASSWORD_ENV' is no longer listed in
  `default_options.h.in'; it is no longer meant to be set by the user, and
  is instead left to be defined in `sysoptions.h' (where it was already being
  defined) as merely the name of the environment variable in question:

    DROPBEAR_PASSWORD

  To enable or disable use of that environment variable, the user must now
  toggle `DROPBEAR_USE_DROPBEAR_PASSWORD'.

* The sFTP support is now toggled by setting `DROPBEAR_SFTPSERVER', and the
  path of the sFTP server program is set independently through the usual
  SFTPSERVER_PATH.

1 files changed, 3 insertions, 3 deletions

diff --git a/signkey.c b/signkey.c
index 682d445..d33ef44 100644
--- a/signkey.c
+++ b/signkey.c
@@ -78,13 +78,13 @@ enum signkey_type signkey_type_from_name(const char* name, unsigned int namelen)
 #if DROPBEAR_ECDSA
 			/* Some of the ECDSA key sizes are defined even if they're not compiled in */
 			if (0
-#ifndef DROPBEAR_ECC_256
+#if !DROPBEAR_ECC_256
 				|| i == DROPBEAR_SIGNKEY_ECDSA_NISTP256
 #endif
-#ifndef DROPBEAR_ECC_384
+#if !DROPBEAR_ECC_384
 				|| i == DROPBEAR_SIGNKEY_ECDSA_NISTP384
 #endif
-#ifndef DROPBEAR_ECC_521
+#if !DROPBEAR_ECC_521
 				|| i == DROPBEAR_SIGNKEY_ECDSA_NISTP521
 #endif
 				) {