Rework subversion <svn> tasks

[rmboggs]

Now would be a good time to upgrade the tasks to use SharpSvn libs so it no longer relies on using the exec task.

[rmboggs]

A good example of how the <svn> task can be restructured can be found here

Basically, the svn commands would be elements for the <svn> task:

  <svn>
      <add dir="workingcopy/propTest"/>
      <commit message="propTest added" dir="workingcopy/propTest"/>
      <propset 
          path="workingcopy/propTest/file.png" 
          name="svn:mime-type" 
          value="image/png"
      />
      <propset 
          path="workingcopy/propTest/file.png" 
          name="myPicture" 
          file="workingcopy/propTest/icon.gif"
      />
  </svn>