In unzip_file(), confirm we have enough available disk space before extracting.

"enough" is calculated by adding up the uncompressed size of the files in the archive, then adding a 20% buffer.

props dd32.
fixes #25576.


git-svn-id: https://develop.svn.wordpress.org/trunk@25774 602fd350-edb4-49c9-b593-d223f7449a82
In the upgrader, only print additional error data if it is a string.

As in [25576], we sometimes want to return additional data that is not necessarily meant for UI consumption.

see #25576.


git-svn-id: https://develop.svn.wordpress.org/trunk@25775 602fd350-edb4-49c9-b593-d223f7449a82