Delay removing files in case of RTF till end of process

In case we include a file by means of a `\rtfonly` section like:
```
\rtfonly
\par \pard\plain
{\field\fldedit{\*\fldinst INCLUDETEXT "inc_aa.rtf" \\*MERGEFORMAT}{\fldrslt includedstuff}}
\endrtfonly
```
or
```
\rtfonly
\par \pard\plain
{\field\fldedit{\*\fldinst INCLUDETEXT "../inc_aa1.rtf" \\*MERGEFORMAT}{\fldrslt includedstuff}}
\endrtfonly
```

we get errors when a file is included multiple times or for the relative link on the second invocation as the files are removed directly after been included.
This is not desirable.
- remove files just at the end of the merging process
- only remove files in the `RTF_OUTPUT` directory (this will contain only "generated / copied" files)
- create possibility to have "RTF_EXTRA_FILES` analogous to the HTML and LATEX counterparts.

src/config.xml

@@ -3328,6 +3328,17 @@ The following block name is set based on whether or not a feature is used in the
  Syntax is similar to doxygen's configuration file.
  A template extensions file can be generated using
  <code>doxygen -e rtf extensionFile</code>.
+]]>
+      </docs>
+    </option>
+    <option type='list' id='RTF_EXTRA_FILES' format='file' depends='GENERATE_RTF'>
+      <docs>
+<![CDATA[
+ The \c RTF_EXTRA_FILES tag can be used to specify one or more extra images
+ or other source files which should be copied to the \ref cfg_rtf_output "RTF_OUTPUT"
+ output directory.
+ Note that the files will be copied as-is; there are no commands or markers
+ available.
 ]]>
       </docs>
     </option>

src/doxygen.cpp

@@ -12544,6 +12544,7 @@ void generateOutput()
   {
     copyLogo(Config_getString(RTF_OUTPUT));
     copyIcon(Config_getString(RTF_OUTPUT));
+    copyExtraFiles(Config_getList(RTF_EXTRA_FILES),"RTF_EXTRA_FILES",Config_getString(RTF_OUTPUT));
   }
 
   FormulaManager &fm = FormulaManager::instance();

src/rtfgen.cpp

@@ -53,6 +53,8 @@
 //#define DBG_RTF(x) x;
 #define DBG_RTF(x)
 
+static StringSet removeSet;
+
 static QCString dateToRTFDateString()
 {
   auto tm = getCurrentDateTime();
@@ -2204,7 +2206,7 @@ static void encodeForOutput(TextStream &t,const QCString &s)
  * VERY brittle routine inline RTF's included by other RTF's.
  * it is recursive and ugly.
  */
-static bool preProcessFile(Dir &d,const QCString &infName, TextStream &t, bool bIncludeHeader=TRUE)
+static bool preProcessFile(Dir &d,const QCString &infName, TextStream &t, bool bIncludeHeader=true, bool removeFile = true)
 {
   static bool rtfDebug = Debug::isFlagSet(Debug::Rtf);
   std::ifstream f = Portable::openInputStream(infName);
@@ -2267,7 +2269,7 @@ static bool preProcessFile(Dir &d,const QCString &infName, TextStream &t, bool b
   }
   f.close();
   // remove temporary file
-  if (!rtfDebug) d.remove(infName.str());
+  if (!rtfDebug && removeFile) removeSet.insert(FileInfo(d.filePath(infName.str())).absFilePath());
   return TRUE;
 }
 
@@ -2419,6 +2421,8 @@ void testRTFOutput(const QCString &name)
 bool RTFGenerator::preProcessFileInplace(const QCString &path,const QCString &name)
 {
   static bool rtfDebug = Debug::isFlagSet(Debug::Rtf);
+  QCString rtfOutput = Config_getString(RTF_OUTPUT);
+
   Dir d(path.str());
   // store the original directory
   if (!d.exists())
@@ -2444,12 +2448,12 @@ bool RTFGenerator::preProcessFileInplace(const QCString &path,const QCString &na
   }
   TextStream outt(&f);
 
-  if (!preProcessFile(thisDir,mainRTFName,outt))
+  if (!preProcessFile(thisDir,mainRTFName,outt,true,false))
   {
     // it failed, remove the temp file
     outt.flush();
     f.close();
-    if (!rtfDebug) thisDir.remove(combinedName.str());
+    if (!rtfDebug) removeSet.insert(FileInfo(thisDir.filePath(combinedName.str())).absFilePath());
     Dir::setCurrent(oldDir);
     return FALSE;
   }
@@ -2469,6 +2473,12 @@ bool RTFGenerator::preProcessFileInplace(const QCString &path,const QCString &na
 
   testRTFOutput(mainRTFName);
 
+  for (auto &s : removeSet)
+  {
+    QCString s1(s.c_str());
+    if (s1.startsWith(rtfOutput)) Portable::unlink(s1);
+  }
+
   Dir::setCurrent(oldDir);
   return TRUE;
 }