shells/bash has an unhandled dependency on libiconv.

Fix: 

Make shells/bash depend on converters/libiconv, or else fix the broken
vendor makefile to not link against libiconv when configure doesn't
find it.  It builds just fine without it.
How-To-Repeat: Attempt to build shells/bash on a machine with no libiconv.  Watch it
fail:

[root@ca /usr/ports/shells/bash]# make
===>  Building for bash-4.1.7
rm -f bash
cc -L./builtins -L./lib/readline -L./lib/readline -L./lib/glob  -L./lib/tilde  -L./lib/sh -L/usr/local/lib  -rdynamic  -O -pipe -o bash shell.o eval.o y.tab.o general.o make_cmd.o print_cmd.o   dispose_cmd.o execute_cmd.o variables.o copy_cmd.o error.o  expr.o flags.o jobs.o subst.o hashcmd.o hashlib.o mailcheck.o  trap.o input.o unwind_prot.o pathexp.o sig.o test.o version.o  alias.o array.o arrayfunc.o assoc.o braces.o bracecomp.o bashhist.o  bashline.o  list.o stringlib.o locale.o findcmd.o redir.o  pcomplete.o pcomplib.o syntax.o xmalloc.o  -lbuiltins -lglob -lsh -lreadline -lhistory -ltermcap  -ltilde   -liconv 
/usr/bin/ld: cannot find -liconv
*** Error code 1