Replaced the complex implementation of valueToString(double).

The previous one was confusing and prone to buffer overflows, and didn't
work correctly with 16-decimal-digit numbers. The new one simply uses
snprintf with a standard format string.

The major change is that we don't always print a decimal point now.
Fortunately, JSON doesn't distinguish between integers and reals.

src/lib_json/json_writer.cpp

@@ -73,40 +73,19 @@ std::string valueToString( UInt value )
 
 std::string valueToString( double value )
 {
+   // Allocate a buffer that is more than large enough to store the 16 digits of
+   // precision requested below.
    char buffer[32];
+
+   // Print into the buffer. We need not request the alternative representation
+   // that always has a decimal point because JSON doesn't distingish the
+   // concepts of reals and integers.
 #if defined(_MSC_VER) && defined(__STDC_SECURE_LIB__) // Use secure version with visual studio 2005 to avoid warning. 
-   sprintf_s(buffer, sizeof(buffer), "%#.16g", value); 
-#else	
-   snprintf(buffer, sizeof(buffer), "%#.16g", value);
+   sprintf_s(buffer, sizeof(buffer), "%.16g", value); 
+#else
+   snprintf(buffer, sizeof(buffer), "%.16g", value);
 #endif
-   char* ch = buffer + strlen(buffer) - 1;
-   if (*ch != '0') return buffer; // nothing to truncate, so save time
-   while(ch > buffer && *ch == '0'){
-     --ch;
-   }
-   char* last_nonzero = ch;
-   while(ch >= buffer){
-     switch(*ch){
-     case '0':
-     case '1':
-     case '2':
-     case '3':
-     case '4':
-     case '5':
-     case '6':
-     case '7':
-     case '8':
-     case '9':
-       --ch;
-       continue;
-     case '.':
-       // Truncate zeroes to save bytes in output, but keep one.
-       *(last_nonzero+2) = '\0';
-       return buffer;
-     default:
-       return buffer;
-     }
-   }
+
    return buffer;
 }