Add Fl_String not-equal test

src/Fl_String.H

@@ -135,6 +135,7 @@ public:
 FL_EXPORT Fl_String operator+(const Fl_String& lhs, const Fl_String& rhs);
 FL_EXPORT Fl_String operator+(const Fl_String& lhs, const char* rhs);
 FL_EXPORT bool operator==(const Fl_String & lhs, const Fl_String & rhs);
+FL_EXPORT bool operator!=(const Fl_String & lhs, const Fl_String & rhs);
 
 /**
 \}

src/Fl_String.cxx

@@ -645,6 +645,19 @@ bool operator==(const Fl_String &lhs, const Fl_String &rhs) {
   return false;
 }
 
+/**
+ Compare two strings for inequality.
+ \param[in] lhs first string
+ \param[in] rhs second string
+ \return true if strings differ in size or content
+ */
+bool operator!=(const Fl_String &lhs, const Fl_String &rhs) {
+  if (lhs.size() != rhs.size()) return true;
+  int sz = lhs.size();  // same size for both
+  if (memcmp(lhs.data(), rhs.data(), sz) != 0) return true;
+  return false;
+}
+
 /**
 \}
 \endcond

test/unittest_core.cxx

@@ -193,6 +193,8 @@ TEST(Fl_String, Non-Member Functions) {
   EXPECT_STREQ(result.c_str(), "x");
   EXPECT_TRUE(!(a == b));
   EXPECT_TRUE(a == a);
+  EXPECT_FALSE((a != a));              // neq -erco
+  EXPECT_TRUE((a != b));               // neq -erco
   EXPECT_TRUE(empty == empty);
   EXPECT_TRUE(a+b == "ab");
   EXPECT_TRUE(a+"b" == "a" + b);