Logging API changes

Remove would_log() : callbacks receive all log messages so they can
do custom filtering individually.

Also move popup message handling into the private (d-ptr) of sglog(),
to keep the header as minimal impossible (no include of <vector>)

simgear/debug/BufferedLogCallback.cxx

@@ -52,11 +52,11 @@ BufferedLogCallback::BufferedLogCallback(sgDebugClass c, sgDebugPriority p) :
 
 BufferedLogCallback::~BufferedLogCallback()
 {
-    BOOST_FOREACH(unsigned char* msg, d->m_buffer) {
+    for (unsigned char* msg : d->m_buffer) {
         free(msg);
     }
 }
- 
+    
 void BufferedLogCallback::operator()(sgDebugClass c, sgDebugPriority p, 
         const char* file, int line, const std::string& aMessage)
 {