Make profiling correctly handle opening the same file multiple times

This patch ensures when reopening a file we check if the filename
has been opened previously, and if so associate it with the same
filename number.

This is tested in the 'profiling' package, which is why there is no
tests here.

src/code.c

@@ -42,6 +42,8 @@
 
 #include        "code.h"                /* coder                           */
 
+#include        "bool.h"                /* For fail                        */
+
 #include        "saveload.h"            /* saving and loading              */
 #include        "read.h"                /* to access stack of for loop globals */
 #include        "gvars.h"
@@ -120,14 +122,23 @@ static inline void PopLoopNesting( void ) {
 static inline void setup_gapname(TypInputFile* i)
 {
   UInt len;
+  Obj pos;
   if(!i->gapname) {
     C_NEW_STRING_DYN(i->gapname, i->name);
-    len = LEN_PLIST( FilenameCache );
-    GROW_PLIST(      FilenameCache, len+1 );
-    SET_LEN_PLIST(   FilenameCache, len+1 );
-    SET_ELM_PLIST(   FilenameCache, len+1, i->gapname );
-    CHANGED_BAG(     FilenameCache );
-    i->gapnameid = len+1;
+    pos = POS_LIST( FilenameCache, i->gapname, INTOBJ_INT(1) );
+    if(pos == Fail) {
+        len = LEN_PLIST( FilenameCache );
+        GROW_PLIST(      FilenameCache, len+1 );
+        SET_LEN_PLIST(   FilenameCache, len+1 );
+        SET_ELM_PLIST(   FilenameCache, len+1, i->gapname );
+        CHANGED_BAG(     FilenameCache );
+        i->gapnameid = len + 1;
+    }
+    else {
+        i->gapnameid = INT_INTOBJ(pos);
+        // Use string from FilenameCache as we know it will not get GCed
+        i->gapname = ELM_LIST( FilenameCache, i->gapnameid );
+    }
   }
 }