Do not allow blockfile pruning during reindex.

Also clarify startup message.

Github-Pull: #6856
Rebased-From: d3b09f6bac738958b6bf5711bcb5291049b7466d

src/main.cpp

@@ -2000,7 +2000,7 @@ bool static FlushStateToDisk(CValidationState &state, FlushStateMode mode) {
     std::set<int> setFilesToPrune;
     bool fFlushForPrune = false;
     try {
-    if (fPruneMode && fCheckForPruning) {
+    if (fPruneMode && fCheckForPruning && !fReindex) {
         FindFilesToPrune(setFilesToPrune);
         fCheckForPruning = false;
         if (!setFilesToPrune.empty()) {