Add explicit casts from boost::tribool to bool.  Starting with 1.69,
tribool added 'explicit' to the conversion operator to bool, and this
was breaking the build when using boost >= 1.69.

Patch is from:  https://github.com/dyninst/dyninst/commit/54a2debd9


diff --git a/dataflowAPI/rose/util/Message.C b/dataflowAPI/rose/util/Message.C
index a8a66ad4c..5e276f97d 100644
--- a/dataflowAPI/rose/util/Message.C
+++ b/dataflowAPI/rose/util/Message.C
@@ -1123,7 +1123,7 @@ StreamBuf::bake() {
         destination_->bakeDestinations(message_.properties(), baked_/*out*/);
         anyUnbuffered_ = false;
         for (BakedDestinations::const_iterator bi=baked_.begin(); bi!=baked_.end() && !anyUnbuffered_; ++bi)
-            anyUnbuffered_ = !bi->second.isBuffered;
+            anyUnbuffered_ = static_cast<bool>(!bi->second.isBuffered);
         isBaked_ = true;
     }
 }
diff --git a/dataflowAPI/rose/util/Message.h b/dataflowAPI/rose/util/Message.h
index 816f68d2e..03592cb97 100644
--- a/dataflowAPI/rose/util/Message.h
+++ b/dataflowAPI/rose/util/Message.h
@@ -386,7 +386,8 @@ struct SAWYER_EXPORT ColorSpec {
     ColorSpec(AnsiColor fg, AnsiColor bg, bool bold): foreground(fg), background(bg), bold(bold) {}
 
     /** Returns true if this object is in its default-constructed state. */
-    bool isDefault() const { return COLOR_DEFAULT==foreground && COLOR_DEFAULT==background && !bold; }
+    bool isDefault() const { return COLOR_DEFAULT==foreground && COLOR_DEFAULT==background
+                                    && static_cast<bool>(!bold); }
 };
 
 /** Colors to use for each message importance.