PT-2378 - extended FP precision in pt-table-sync

pt-table-sync now uses up to 17 decimal digits when writing
floating point numbers in the generated SQL statements.
This is necessary to prevent unintended data changes.

bin/pt-table-usage

@@ -6680,7 +6680,10 @@ sub quote_val {
    return $val if $val =~ m/^0x[0-9a-fA-F]+$/  # quote hex data
                   && !$args{is_char};          # unless is_char is true
 
-   return $val if $args{is_float};
+   if ( $args{is_float} ) {
+      return sprintf("%.17g", $val) if $val - "$val" != 0;
+      return $val;
+   }
 
    $val =~ s/(['\\])/\\$1/g;
    return "'$val'";