get_rnd_text() for rumors and other stuff

Solve the uneven distribution situation that has been present for
picking random rumors for a long time and for random engravings,
epitaphs, and hallucinatory monster names since 3.6.0.  This relies
on the previous partial solution where short lines have been padded
to a longer length.  When that length is N and random seek lands in
a long line of length L, retry if the position is in the first L-N
characters.  Put differently, it if takes more than N characters to
reach the next newline, reject that random seek and try again.  This
effectively makes long lines behave as if they had the same length
of N as the short lines have been padded to and when all lines are
the same length, all entries have the same chance to be chosen.

src/do_name.c

@@ -2204,7 +2204,7 @@ bogusmon(char *buf, char *code)
     if (code)
         *code = '\0';
     /* might fail (return empty buf[]) if the file isn't available */
-    get_rnd_text(BOGUSMONFILE, buf, rn2_on_display_rng);
+    get_rnd_text(BOGUSMONFILE, buf, rn2_on_display_rng, MD_PAD_BOGONS);
     if (!*mnam) {
         Strcpy(buf, "bogon");
     } else if (index(bogon_codes, *mnam)) { /* strip prefix if present */