Update tools versioning and libsodium paths.

This updates the GSL templates to emit VS2010 and VS2012 project files with tools version set to 4.0. This will prevent a warning upon compile when the 12.0 tools are not installed.

This also reverts a path change to the existing VS2010 libsodium outputs. I am anticipating that libsodium will soon merge the pull request that updates these paths and also adds support for VS2012 and VS2013. In the mean time a workaround is to pull libsodium from [my fork](https://github.com/evoskuil/libsodium). This would be required for the VS2012 and VS2013 builds in any case, since libsodium does not yet include those platforms.