War on -Werror, part 12: explicit bool usage.

It may save a few cycles, but it's best to be
explicit on boolean operations, especially with
ASSERT.

src/TrailUtil.cpp

@@ -39,7 +39,7 @@ void TrailID::FromTrail( const Trail *p )
 
 Trail *TrailID::ToTrail( const Course *p, bool bAllowNull ) const
 {
-	ASSERT( p );
+	ASSERT( p != NULL );
 
 	Trail *pRet = NULL;
 	if( !m_Cache.Get(&pRet) )