Add strutils::iequals helper

Replaces another boost method

simgear/misc/strutils.cxx

@@ -624,6 +624,22 @@ namespace simgear {
       }
     }
         
+        
+bool iequals(const std::string& a, const std::string& b)
+{
+    const auto lenA = a.length();
+    const auto lenB = b.length();
+    if (lenA != lenB) return false;
+    
+    const char* aPtr = a.data();
+    const char* bPtr = b.data();
+    for (size_t i = 0; i < lenA; ++i) {
+        if (tolower(*aPtr++) != tolower(*bPtr++)) return false;
+    }
+    
+    return true;
+}
+
 #if defined(SG_WINDOWS)
 static std::wstring convertMultiByteToWString(DWORD encoding, const std::string& a)
 {

simgear/misc/strutils.hxx

@@ -264,6 +264,11 @@ namespace simgear {
    */
   void lowercase(std::string &s);
   
+      /**
+       * case-insensitive string comparisom
+       */
+      bool iequals(const std::string& a, const std::string& b);
+      
 	/**
      * convert a string in the local Windows 8-bit encoding to UTF-8
      * (no-op on other platforms)

simgear/misc/strutils_test.cxx

@@ -99,6 +99,16 @@ void test_to_int()
   SG_CHECK_EQUAL(strutils::to_int("-10000"), -10000);
 }
 
+void test_iequals()
+{
+    SG_VERIFY(strutils::iequals("abcdef", "AbCDeF"));
+    SG_VERIFY(strutils::iequals("", ""));
+    SG_VERIFY(!strutils::iequals("abcdE", "ABCD"));
+    SG_VERIFY(strutils::iequals("%$abcdef12", "%$AbCDeF12"));
+    SG_VERIFY(strutils::iequals("VOR-DME", "vor-dme"));
+    SG_VERIFY(!strutils::iequals("VOR-DME", "vor_dme"));
+}
+
 // Auxiliary function for test_readNonNegativeInt()
 void aux_readNonNegativeInt_setUpOStringStream(std::ostringstream& oss, int base)
 {
@@ -737,6 +747,7 @@ int main(int argc, char* argv[])
     test_utf8Convert();
     test_parseGeod();
     test_formatGeod();
+    test_iequals();
     
     return EXIT_SUCCESS;
 }