Significant refactoring:

- Support for error objects crossing DLL boundaries on Windows via BOOST_LEAF_CFG_WIN32=2.
- Internal TLS interface improvements, separating logical allocation from reading.
- Dynamic allocations (if enabled) for on_error objects now happens before stack unwinding begins.
- BOOST_LEAF_SYMBOL_VISIBLE declarations now separated in config/visibility.hpp.

test/multiple_errors_test.cpp

@@ -13,7 +13,6 @@
 #endif
 
 #include "lightweight_test.hpp"
-#include <exception>
 
 namespace leaf = boost::leaf;