Misc small fixes to suppress warnings.

Code should now be clean with msvc /W4 and gcc /Wall /Wextra -pedantic with the exception of one deliberate warning in one test.

[SVN r57510]

test/implicit_cast.cpp

@@ -28,5 +28,11 @@ int main()
 
     type<foo> f = check_return(boost::implicit_cast<foo>("hello"));
     type<long> z = check_return(boost::implicit_cast<long>(foo("hello")));
+    
+    // warning supression:
+    (void)x;
+    (void)f;
+    (void)z;
+
     return boost::report_errors();
 }