Improve sgstream_test.cxx

- Create "testfile" in a temporary directory (and make sure the temp dir
  and the file it contains are both removed when the test program exits).

- Use test macros such as SG_CHECK_EQUAL() instead of by-hand checks and
  "return EXIT_FAILURE" statements.

- Use sg_ofstream instead of plain std::ostream. This simplifies things
  a tiny bit, because one SGPath instance is enough to create both the
  sg_ofstream instance and the sg_gzifstream instance used afterwards to
  reread the created file.

- Don't call (sg_)ofstream::close() at the end of the block the instance
  is declared in: this is entirely unnecessary, since sg_ofstream
  derives from std::ofstream, which is automatically close()d when
  destroyed (RAII behavior).

simgear/misc/sgstream_test.cxx

@@ -1,52 +1,53 @@
 #include <iostream>
-#include <fstream>
+#include <cstdlib> // for EXIT_SUCCESS
 
-#include <cstdlib> // for EXIT_FAILURE
-
-using std::ofstream;
+using std::string;
 using std::cout;
 using std::endl;
 
+#include <simgear/misc/test_macros.hxx>
 #include <simgear/misc/sgstream.hxx>
 #include <simgear/misc/sg_path.hxx>
+#include <simgear/misc/sg_dir.hxx>
 
 int main()
 {
-    const char* fileName = "testfile";
+    const string fileName = "testfile";
+    simgear::Dir tmpDir = simgear::Dir::tempDir("FlightGear");
+    tmpDir.setRemoveOnDestroy();
+    SGPath p(tmpDir.path() / fileName);
+
     {
-       ofstream f;
-       f.open(fileName, std::ios::binary | std::ios::trunc | std::ios::out);
+       sg_ofstream f(p, std::ios::binary | std::ios::trunc | std::ios::out);
        f.write("first line ends with line-feed\n"
            "second line ends with just a cr\r"
            "third line ends with both\r\n"
            "fourth line as well\r\n"
            "fifth line is another CR/LF line\r\n"
            "end of test\r\n", 158);
-       f.close();
-   }
+    }
 
-    SGPath p(fileName);
    sg_gzifstream sg(p);
    std::string stuff;
    sg >> skipeol;
    sg >> stuff;
-   if (stuff != "second") return EXIT_FAILURE;
+   SG_CHECK_EQUAL(stuff, "second");
    cout << "Detection of LF works." << endl;
 
    sg >> skipeol;
    sg >> stuff;
-   if (stuff != "third") return EXIT_FAILURE;
+   SG_CHECK_EQUAL(stuff, "third");
    cout << "Detection of CR works." << endl;
 
    sg >> skipeol;
    sg >> stuff;
-   if (stuff != "fourth") return EXIT_FAILURE;
+   SG_CHECK_EQUAL(stuff, "fourth");
    cout << "Detection of CR/LF works." << endl;
 
    sg >> skipeol;
    sg >> skipeol;
    sg >> stuff;
-   if (stuff != "end") return EXIT_FAILURE;
+   SG_CHECK_EQUAL(stuff, "end");
    cout << "Detection of 2 following CR/LF lines works." << endl;
 
    return EXIT_SUCCESS;