Fixed usage of DateTime#sec_fraction

Hello.  I have been upgrading an application from Ruby 1.8.7 to Ruby 1.9.3 and working on using the mumboe-soap4r gem for our SOAP requests.  Unfortunately, I encountered a bug in the way that dates are formatted, which caused the application to submit invalid date strings like the following to the remote server:

```2013-01-18T15:37:1645505.8806112000020221-08:00```

The DateTime#sec_fraction method has units of seconds in Ruby 1.9.3, not days, as demonstrated in [this gist](https://gist.github.com/1274588). I am assuming we don't care about this gem working with Ruby 1.8, so I just removed the code that multiplies by `DayInSec` when formatting a fractional second.  I also made some other minor changes to help maintain the gem, and you can read more about those in my commit messages.  Please merge these in if you think they are good!

Based on the [download stats at rubygems.org](http://rubygems.org/search?query=soap), it looks like your `mumboe-soap4r` gem is the most popular SOAP gem for ruby 1.9 that is a fork of soap4r.  Congratulations, and thank you for the work you have done on this gem!  That being said, I noticed that the test suite is not being maintained.  I had to make some changes to `test/runner.rb` to run the tests, and when I did run the tests I got "307 tests, 1783 assertions, 12 failures, 175 errors, 0 skips".  I would encourage you to work on fixing those tests, but I understand that you probably don't have much of a reason to do all that work for free.

Also, a minor note, the link in the README.rdoc is broken: http://dev.ctor.org/soap4r seems to have disappeared.

Thanks!

--David