all: Remove lib/util package (#9049)

Grab-bag packages are nasty, this cleans it up a little by splitting it
into topical packages sempahore, netutil, stringutil, structutil.

lib/stringutil/stringutil_test.go

@@ -0,0 +1,51 @@
+// Copyright (C) 2016 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package stringutil
+
+import (
+	"testing"
+)
+
+func TestUniqueStrings(t *testing.T) {
+	tests := []struct {
+		input    []string
+		expected []string
+	}{
+		{
+			[]string{"a", "b"},
+			[]string{"a", "b"},
+		},
+		{
+			[]string{"a", "a"},
+			[]string{"a"},
+		},
+		{
+			[]string{"a", "a", "a", "a"},
+			[]string{"a"},
+		},
+		{
+			nil,
+			nil,
+		},
+		{
+			[]string{"       a     ", "     a  ", "b        ", "    b"},
+			[]string{"a", "b"},
+		},
+	}
+
+	for _, test := range tests {
+		result := UniqueTrimmedStrings(test.input)
+		if len(result) != len(test.expected) {
+			t.Errorf("%s != %s", result, test.expected)
+		}
+		for i := range result {
+			if test.expected[i] != result[i] {
+				t.Errorf("%s != %s", result, test.expected)
+			}
+		}
+	}
+}