tweaks: adjust the type of two arguments

Convert digits() to take a ssize_t instead of an int, since it's
used on ssize_t line numbers.  And properly use the long modifier
when displaying a line number.

Also, conditionalize the digits() prototype.

src/proto.h

@@ -651,7 +651,9 @@ void complete_a_word(void);
 
 /* All functions in utils.c. */
 void get_homedir(void);
-int digits(int n);
+#ifdef ENABLE_LINENUMBERS
+int digits(ssize_t n);
+#endif
 bool parse_num(const char *str, ssize_t *val);
 bool parse_line_column(const char *str, ssize_t *line, ssize_t *column);
 void align(char **str);

src/utils.c

@@ -54,7 +54,7 @@ void get_homedir(void)
 
 #ifdef ENABLE_LINENUMBERS
 /* Return the number of digits that the given integer n takes up. */
-int digits(int n)
+int digits(ssize_t n)
 {
     if (n < 100000) {
         if (n < 1000) {

src/winio.c

@@ -2323,7 +2323,7 @@ void edit_draw(filestruct *fileptr, const char *converted, int
     if (margin > 0) {
 	wattron(edit, interface_color_pair[LINE_NUMBER]);
 	if (last_drawn_line != fileptr->lineno || last_line_y >= line)
-	    mvwprintw(edit, line, 0, "%*i", margin - 1, fileptr->lineno);
+	    mvwprintw(edit, line, 0, "%*ld", margin - 1, (long)fileptr->lineno);
 	else
 	    mvwprintw(edit, line, 0, "%*s", margin - 1, " ");
 	wattroff(edit, interface_color_pair[LINE_NUMBER]);