Fixes for other compilers (#1912)

* remove invalid virtual keywords

* remove duplicate inline

* remove leading 0 in character literals

* add missing public keywords

* fix some struct/class mismatches

include/msg/scrn/d_msg_scrn_explain.h

@@ -4,7 +4,7 @@
 #include "msg/scrn/d_msg_scrn_base.h"
 
 class J2DOrthoGraph;
-struct STControl;
+class STControl;
 class dMsgScrnArrow_c;
 class dMsgScrn3Select_c;
 class dMsgString_c;

include/msg/scrn/d_msg_scrn_tree.h

@@ -3,8 +3,8 @@
 
 #include "msg/scrn/d_msg_scrn_base.h"
 
-struct JUTFont;
-struct JKRExpHeap;
+class JUTFont;
+class JKRExpHeap;
 
 struct dMsgScrnTree_c : public dMsgScrnBase_c {
     /* 80248954 */ dMsgScrnTree_c(JUTFont*, JKRExpHeap*);