partially revert "Switch to copy-and-swap idiom for operator=."

This partially reverts commit 45cd9490cd.

Ignored ValueInternal* changes, since those did not produce symbols for
Debian build. (They must not have used the INTERNAL stuff.)

Ignored CZString changes since those are private (and sizeof struct did
not change).

  https://github.com/open-source-parsers/jsoncpp/issues/78

Conflicts:
	include/json/value.h
	src/lib_json/json_internalarray.inl
	src/lib_json/json_internalmap.inl
	src/lib_json/json_value.cpp

include/json/value.h

@@ -283,7 +283,7 @@ Json::Value obj_value(Json::objectValue); // {}
 
   /// Deep copy, then swap(other).
   /// \note Over-write existing comments. To preserve comments, use #swapPayload().
-  Value& operator=(Value other);
+  Value &operator=(const Value &other);
   /// Swap everything.
   void swap(Value& other);
   /// Swap values but leave comments and source offsets in place.

src/lib_json/json_value.cpp

@@ -466,8 +466,9 @@ Value::~Value() {
     delete[] comments_;
 }
 
-Value& Value::operator=(Value other) {
-  swap(other);
+Value &Value::operator=(const Value &other) {
+  Value temp(other);
+  swap(temp);
   return *this;
 }