Rewrite gprefs() in settings.c so that its input mapping includes

information about where to put items that aren't mentioned in the
saved configuration. So far the only nontrivial use I've made of this
facility is to default to placing KEX_RSA just above KEX_WARN in the
absence of any other information, which should fix
'ssh2-rsa-kex-pref'.

While I'm here I've rewritten wprefs() on general principles to remove
the needless length limit, since I was touching it anyway. The length
limit is still in gprefs (but I've lengthened it just in case).

[originally from svn r9181]

putty.h

@@ -353,12 +353,52 @@ enum {
  * Defined here so that backends can export their GSS library tables
  * to the cross-platform settings code.
  */
-struct keyval { char *s; int v; };
+struct keyvalwhere {
+    /*
+     * Two fields which define a string and enum value to be
+     * equivalent to each other.
+     */
+    char *s;
+    int v;
+
+    /*
+     * The next pair of fields are used by gprefs() in settings.c to
+     * arrange that when it reads a list of strings representing a
+     * preference list and translates it into the corresponding list
+     * of integers, strings not appearing in the list are entered in a
+     * configurable position rather than uniformly at the end.
+     */
+
+    /*
+     * 'vrel' indicates which other value in the list to place this
+     * element relative to. It should be a value that has occurred in
+     * a 'v' field of some other element of the array, or -1 to
+     * indicate that we simply place relative to one or other end of
+     * the list.
+     *
+     * gprefs will try to process the elements in an order which makes
+     * this field work (i.e. so that the element referenced has been
+     * added before processing this one).
+     */
+    int vrel;
+
+    /*
+     * 'where' indicates whether to place the new value before or
+     * after the one referred to by vrel. -1 means before; +1 means
+     * after.
+     *
+     * When vrel is -1, this also implicitly indicates which end of
+     * the array to use. So vrel=-1, where=-1 means to place _before_
+     * some end of the list (hence, at the last element); vrel=-1,
+     * where=+1 means to place _after_ an end (hence, at the first).
+     */
+    int where;
+};
 
 #ifndef NO_GSSAPI
 extern const int ngsslibs;
-extern const char *const gsslibnames[];/* for displaying in configuration */
-extern const struct keyval gsslibkeywords[];   /* for storing by settings.c */
+extern const char *const gsslibnames[]; /* for displaying in configuration */
+extern const struct keyvalwhere gsslibkeywords[]; /* for settings.c */
 #endif
 
 extern const char *const ttymodes[];