Replace CppUnit with Catch for unit tests

Drop the legacy CppUnit testing framework used for the unit tests.
Replacing it with Catch has the advantage of not requiring CppUnit
libraries to be installed on the system in order to be able to run
tests (Catch is header-only and a copy of it is now included in the
main repository itself) and, in the future, of being able to write
the tests in a much more natural way.

For now, however, avoid changing the existing tests code as much as
[reasonably] possible to avoid introducing bugs in them and provide
the CppUnit compatibility macros in the new wx/catch_cppunit.h header
which allow to preserve the 99% of the existing code unchanged. Some
of the required changes are:

 - Decompose asserts using "a && b" conditions into multiple asserts
   checking "a" and "b" independently. This would have been better
   even with CppUnit (to know which part of condition exactly failed)
   and is required with Catch.

 - Use extra parentheses around such conditions when they can't be
   easily decomposed in the arrays test, due to the use of macros.
   This is not ideal from the point of view of messages given when
   the tests fail but will do for now.

 - Rewrite asserts using "a || b" as a combination of condition
   checks and assert macros. Again, this is better anyhow, and is
   required with Catch. Incidentally, this allowed to fix a bug in
   the "exec" unit test which didn't leave enough time for the new
   process to be launched before trying to kill it.

 - Remove multiple CPPUNIT_TEST_SUITE_NAMED_REGISTRATION() macros,
   our emulation of this macro can be used only once.

 - Provide string conversions using Catch-specific StringMaker for
   a couple of types.

 - Replace custom wxImage comparison with a Catch-specific matcher
   class.

 - Remove most of test running logic from test.cpp, in particular don't
   parse command line ourselves any longer but use Catch built-in
   command line parser. This is a source of a minor regression:
   previously, both "Foo" and "FooTestCase" could be used as the name of
   the test to run, but now only the latter is accepted.

tests/events/propagation.cpp

@@ -436,24 +436,14 @@ wxMenu* CreateTestMenu(wxFrame* frame)
 // Helper for checking that the menu event processing resulted in the expected
 // output from the handlers.
 //
-// Notice that this is supposed to be used with ASSERT_MENU_EVENT_RESULT()
-// macro to make the file name and line number of the caller appear in the
-// failure messages.
-void
-CheckMenuEvent(wxMenu* menu, const char* result, CppUnit::SourceLine sourceLine)
-{
-    g_str.clear();
-
-    // Trigger the menu event: this is more reliable than using
-    // wxUIActionSimulator and currently works in all ports as they all call
-    // wxMenuBase::SendEvent() from their respective menu event handlers.
-    menu->SendEvent(wxID_APPLY);
-
-    CPPUNIT_NS::assertEquals( result, g_str, sourceLine, "" );
-}
-
+// Note that we trigger the menu event by sending it directly as this is more
+// reliable than using wxUIActionSimulator and currently works in all ports as
+// they all call wxMenuBase::SendEvent() from their respective menu event
+// handlers.
 #define ASSERT_MENU_EVENT_RESULT(menu, result) \
-    CheckMenuEvent((menu), (result), CPPUNIT_SOURCELINE())
+    g_str.clear();                             \
+    menu->SendEvent(wxID_APPLY);               \
+    CHECK( g_str == result )
 
 void EventPropagationTestCase::MenuEvent()
 {