Unbreak Embarcadero C++ clang-based compilers

* Change __BORLANDC__ to BOOST_BORLANDC, which is defined in Boost config for the Embarcadero non-clang-based compilers.

* Restored a Borland check.

* Specify std:: for all standard identifiers and remove 'using namespace std:'.

* Removed std:: from C header abort call.

* Moved 'using namespace std;' after header file inclusions

Author: eldiener

test/parsers_test.cpp

@@ -308,7 +308,7 @@ void test_environment()
         ("bar", new untyped_value, "")
         ;
 
-#if (defined(_WIN32) && ! defined(__BORLANDC__)) || (defined(__CYGWIN__))
+#if (defined(_WIN32) && ! defined(BOOST_BORLANDC) && ! defined(BOOST_EMBTC)) || (defined(__CYGWIN__))
     _putenv("PO_TEST_FOO=1");
 #else
     putenv(const_cast<char*>("PO_TEST_FOO=1"));

test/winmain.cpp

@@ -9,10 +9,9 @@
 #include <cctype>
 #include <iostream>
 #include <stdlib.h>
+#include <boost/program_options/parsers.hpp>
 
 using namespace std;
-
-#include <boost/program_options/parsers.hpp>
 using namespace boost::program_options;
 
 void check_equal(const std::vector<string>& actual, char **expected, int n)