parseopt: add PARSE_OPT_NODASH

Add support for options that don't start with a dash.  Initially, they
don't accept arguments and can only be short options, i.e. consist of a
single character.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t0040-parse-options.sh

@@ -31,6 +31,7 @@ String options
 Magic arguments
     --quux                means --quux
     -NUM                  set integer to NUM
+    +                     same as -b
 
 Standard options
     --abbrev[=<n>]        use <n> digits to display SHA-1s
@@ -276,6 +277,12 @@ test_expect_success 'OPT_NEGBIT() works' '
 	test_cmp expect output
 '
 
+test_expect_success 'OPT_BOOLEAN() with PARSE_OPT_NODASH works' '
+	test-parse-options + + + + + + > output 2> output.err &&
+	test ! -s output.err &&
+	test_cmp expect output
+'
+
 cat > expect <<EOF
 boolean: 0
 integer: 12345