Update XCProject.cs

添加：
// Delete project file
if( File.Exists( projectPath ))
   File.Delete( projectPath );
修正可能出现的Sharing violation on path Error。另外，整理了一点代码。
Merge pull request #1 from bighard/patch-1

Update XCProject.cs. Add a cleaning before creating project file, in case of a 'Sharing violation on path Error' IOException.