Add opt-in leak detection under MSVC + Windows.

Closes #439

docs/configuration.md

@@ -76,13 +76,16 @@ All C++11 support can be disabled with `CATCH_CONFIG_NO_CPP11`
     CATCH_CONFIG_WINDOWS_SEH                // Enable SEH handling on Windows
     CATCH_CONFIG_FAST_COMPILE               // Sacrifices some (extremely minor) features for compilation speed
     CATCH_CONFIG_POSIX_SIGNALS              // Enable handling POSIX signals
+    CATCH_CONFIG_WINDOWS_CRTDBG             // Enable leak checking using Windows's CRT Debug Heap
 
 Currently Catch enables `CATCH_CONFIG_WINDOWS_SEH` only when compiled with MSVC, because some versions of MinGW do not have the necessary Win32 API support.
 
 At this moment, `CATCH_CONFIG_FAST_COMPILE` changes only the behaviour of the `-b` (`--break`) flag, making it break into debugger in a stack frame *below* the actual test, unlike the default behaviour, where the break into debugger occurs in the same stack frame as the actual test. `CATCH_CONFIG_FAST_COMPILE` has to be either defined, or not defined, in all translation units that are linked into single test binary, or the behaviour of setting `-b` flag will be unpredictable.
 
 `CATCH_CONFIG_POSIX_SIGNALS` is on by default, except when Catch is compiled under `Cygwin`, where it is disabled by default (but can be force-enabled by defining `CATCH_CONFIG_POSIX_SIGNALS`).
 
+`CATCH_CONFIG_WINDOWS_CRTDBG` is off by default. If enabled, it sets Windows's CRT to check for memory leaks, and displays them after the tests finish running.
+
 Just as with the C++11 conformance toggles, these toggles can be disabled by using `_NO_` form of the toggle, e.g. `CATCH_CONFIG_NO_WINDOWS_SEH`.
 
 # Windows header clutter

include/internal/catch_default_main.hpp

@@ -10,8 +10,22 @@
 
 #ifndef __OBJC__
 
+#ifdef CATCH_CONFIG_WINDOWS_CRTDBG
+#include <crtdbg.h>
+#endif
+
 // Standard C/C++ main entry point
 int main (int argc, char * argv[]) {
+#ifdef CATCH_CONFIG_WINDOWS_CRTDBG
+    int flag = _CrtSetDbgFlag(_CRTDBG_REPORT_FLAG);
+    flag |= _CRTDBG_LEAK_CHECK_DF;
+    flag |= _CRTDBG_ALLOC_MEM_DF;
+    _CrtSetDbgFlag(flag);
+    _CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE);
+    _CrtSetReportFile(_CRT_WARN, _CRTDBG_FILE_STDERR);
+    // Change this to leaking allocation's number to break there
+    _CrtSetBreakAlloc(-1);
+#endif
     int result = Catch::Session().run( argc, argv );
     return ( result < 0xff ? result : 0xff );
 }