completion: bash: fix for suboptions with value

We need to ignore options that don't start with -- as well.

Depending on the value of COMP_WORDBREAKS the last word could be
duplicated otherwise.

Can be tested with:

  git merge -X diff-algorithm=<tab>

Tested-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -356,7 +356,7 @@ __gitcomp ()
 	local cur_="${3-$cur}"
 
 	case "$cur_" in
-	--*=)
+	*=)
 		;;
 	--no-*)
 		local c i=0 IFS=$' \t\n'

t/t9902-completion.sh

@@ -540,6 +540,15 @@ test_expect_success '__gitcomp - expand/narrow all negative options' '
 	EOF
 '
 
+test_expect_success '__gitcomp - equal skip' '
+	test_gitcomp "--option=" "--option=" <<-\EOF &&
+
+	EOF
+	test_gitcomp "option=" "option=" <<-\EOF
+
+	EOF
+'
+
 test_expect_success '__gitcomp - doesnt fail because of invalid variable name' '
 	__gitcomp "$invalid_variable_name"
 '
@@ -2380,6 +2389,12 @@ test_expect_success 'git clone --config= - value' '
 	EOF
 '
 
+test_expect_success 'options with value' '
+	test_completion "git merge -X diff-algorithm=" <<-\EOF
+
+	EOF
+'
+
 test_expect_success 'sourcing the completion script clears cached commands' '
 	__git_compute_all_commands &&
 	verbose test -n "$__git_all_commands" &&