Add explicit keyword wherever easily possible

tests/test_file.cpp

@@ -32,7 +32,7 @@ using namespace TagLib;
 // File subclass that gives tests access to filesystem operations
 class PlainFile : public File {
 public:
-  PlainFile(FileName name) : File(name) { }
+  explicit PlainFile(FileName name) : File(name) { }
   Tag *tag() const { return NULL; }
   AudioProperties *audioProperties() const { return NULL; }
   bool save(){ return false; }

tests/test_riff.cpp

@@ -37,7 +37,7 @@ using namespace TagLib;
 class PublicRIFF : public RIFF::File
 {
 public:
-  PublicRIFF(FileName file) : RIFF::File(file, BigEndian) {};
+  explicit PublicRIFF(FileName file) : RIFF::File(file, BigEndian) {};
   unsigned int riffSize() { return RIFF::File::riffSize(); };
   size_t chunkCount() { return RIFF::File::chunkCount(); };
   long long chunkOffset(unsigned int i) { return RIFF::File::chunkOffset(i); };

tests/test_smartptr.cpp

@@ -92,7 +92,7 @@ private:
   class DummyBase
   {
   public:
-    DummyBase(int x) : value(x)
+    explicit DummyBase(int x) : value(x)
     {
     }
   
@@ -113,7 +113,7 @@ private:
   class DummyDerived : public DummyBase
   {
   public:
-    DummyDerived(int x) : DummyBase(x)
+    explicit DummyDerived(int x) : DummyBase(x)
     {
     }