Basic support for custom completion handlers with the two "standard"

rl_complete() and rl_list_possib().  Simply leave out complete.o from
the default build and in all programs require these two functions to
be supplied.

A better alternative would be to use function pointers and check those
for NULL in the running code.  With this code, and no completion handler
the editline code will die.

examples/cli.c

@@ -0,0 +1,78 @@
+/* The "testit" micro shell, now with command completion. 
+ * To be able to run, don't "--enable-default-complete".
+ */
+#include "editline.h"
+#include <string.h>
+
+char *list[] = {
+   "foo ", "bar ", "bsd ", "cli ", "ls ", "cd ", "malloc ", "tee ", NULL
+};
+
+/*
+**  Attempt to complete the pathname, returning an allocated copy.
+**  Fill in *unique if we completed it, or set it to 0 if ambiguous.
+*/
+char *rl_complete(char *token, int *match)
+{
+   int i;
+   int index = -1;
+   int matchlen = 0;
+   int count = 0;
+
+   for (i = 0; list[i]; i++)
+   {
+      int partlen = strlen (token); /* Part of token */
+
+      if (!strncmp (list[i], token, partlen))
+      {
+         index = i;
+         matchlen = partlen;
+         count ++;
+      }
+   }
+
+   if (count == 1)
+   {
+      *match = 1;
+      return strdup (list[index] + matchlen);
+   }
+
+   return NULL;
+}
+
+/*
+**  Return all possible completions.
+*/
+int rl_list_possib(char *token, char ***av)
+{
+   int i, num, total = 0;
+   char **copy;
+   
+   for (num = 0; list[num]; num++)
+      ;
+   copy = (char **) malloc (num * sizeof(char *));
+   for (i = 0; i < num; i++)
+   {
+      if (!strncmp (list[i], token, strlen (token)))
+      {
+         copy[total] = strdup (list[i]);
+         total ++;
+      }
+   }
+   *av = copy;
+
+   return total;
+}
+
+int main(int ac, char *av[])
+{
+   char *line;
+   char	*prompt = "cli> ";
+
+   while ((line = readline(prompt)) != NULL) {
+      (void)printf("\t\t\t|%s|\n", line);
+      free(line);
+   }
+
+   return 0;
+}