fixed handling of nuget packages

Having packages/ as the ignore line without a * meant the entire packages folder got ignored, and no attention paid to the following line !packages/repositories.config as the folder itself was ignored. The * forces the ignore to the packages folder contents.

Also needed to change the syntax and bring the !packages/build/ line further down. The earlier syntax was not working as files in packages/build/ were not being staged, and also it needed to be applied after the ignore of packages folder has been applied, so that it can override the exclusion of the packages folder