Reduce compiler.h to almost nothing (but it's worth keeping around I think, for

the MSVC and MipsPro warning stuff).

As a result of this patch, simgear/sg_traits.h can be deleted. So can SGCMath.h,
but I'll do that separately.

There is one more 'mechanical' change to come - getting rid of SG_USING_STD(X),
but I want to keep that separate from everything else. (There's another mechnica
l change, replacing <math.h> with <cmath> and so on *everywhere*, but one step a
t a time)

simgear/xml/easyxml.cxx

@@ -11,8 +11,8 @@
 #include "easyxml.hxx"
 #include "xmlparse.h"
 
-#include STL_FSTREAM
-#include STL_IOSTREAM
+#include <fstream>
+#include <iostream>
 
 SG_USING_STD(ifstream);
 

simgear/xml/easyxml.hxx

@@ -11,8 +11,8 @@
 #include <simgear/compiler.h>
 #include <simgear/structure/exception.hxx>
 
-#include STL_IOSTREAM
-#include STL_STRING
+#include <iostream>
+#include <string>
 #include <vector>
 
 SG_USING_STD(istream);