Add support for SQL_WLONGVARCHAR data type

SQL Server, for example, reports
- `NTEXT` as `SQL_WLONGVARCHAR`
- `TEXT` as `SQL_LONGVARCHAR`

Formerly, `SQL_WLONGVARCHAR` column was only recognised by accident
due to defined `SQL_NVARCHAR(-10)` but the implementation was broken:
- `SQLDescribeCol` returns the column size of 1073741824 characters
- The column was not recognised as large variable-length object
- The column was also incorrectly recognised as `SQLCHAR`-based data
- Binding would attempt to pre-allocate large buffer of size
  `sizeof(SQLCHAR) * 1073741824`

Removal of the `SQL_NVARCHAR` proposed in #210 - which is
a requirement of this changeset.

nanodbc/nanodbc.cpp

@@ -2834,6 +2834,11 @@ class result::result_impl
                 col.blob_ = true;
                 col.clen_ = 0;
                 break;
+            case SQL_WLONGVARCHAR:
+                col.ctype_ = sql_ctype<wide_string>::value;
+                col.blob_ = true;
+                col.clen_ = 0;
+                break;
             case SQL_BINARY:
             case SQL_VARBINARY:
             case SQL_LONGVARBINARY:

test/mssql_test.cpp

@@ -517,6 +517,46 @@ TEST_CASE_METHOD(mssql_fixture, "test_string_with_varchar_max", "[mssql][string]
     test_string_with_varchar_max();
 }
 
+TEST_CASE_METHOD(mssql_fixture, "test_string_with_ntext", "[mssql][string][ntext]")
+{
+    nanodbc::connection connection = connect();
+    drop_table(connection, NANODBC_TEXT("test_string_with_ntext"));
+    execute(
+        connection, NANODBC_TEXT("create table test_string_with_ntext (s ntext);"));
+    execute(
+        connection,
+        NANODBC_TEXT("insert into test_string_with_ntext(s) ")
+            NANODBC_TEXT("values (REPLICATE(CAST(\'a\' AS nvarchar(MAX)), 15000))"));
+
+    nanodbc::result results =
+        execute(connection, NANODBC_TEXT("select s from test_string_with_ntext;"));
+    REQUIRE(results.next());
+
+    nanodbc::string select;
+    results.get_ref(0, select);
+    REQUIRE(select.size() == 15000);
+}
+
+TEST_CASE_METHOD(mssql_fixture, "test_string_with_text", "[mssql][string][text]")
+{
+    nanodbc::connection connection = connect();
+    drop_table(connection, NANODBC_TEXT("test_string_with_text"));
+    execute(
+        connection, NANODBC_TEXT("create table test_string_with_text (s text);"));
+    execute(
+        connection,
+        NANODBC_TEXT("insert into test_string_with_text(s) ")
+            NANODBC_TEXT("values (REPLICATE(CAST(\'a\' AS varchar(MAX)), 15000))"));
+
+    nanodbc::result results =
+        execute(connection, NANODBC_TEXT("select s from test_string_with_text;"));
+    REQUIRE(results.next());
+
+    nanodbc::string select;
+    results.get_ref(0, select);
+    REQUIRE(select.size() == 15000);
+}
+
 TEST_CASE_METHOD(mssql_fixture, "test_string_vector", "[mssql][string]")
 {
     test_string_vector();