Check the available disk space before attempting upgrades

[dd32]

At present we attempt to upgrade WordPress without first checking that there's enough space to uncompress the archive into the working directory.

Attached is a patch to check the disk space prior to Zip extraction, It only checks there's enough space to extract into the Working directory (which is in WP_CONTENT_DIR/upgrade).

[nacin]

In 25774:

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.

[nacin]

In 25775:

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.

[nacin]

In 25776:

Account for possible failures by disk_free_space(), as well as the potential need to copy the unzipped files.

see #25576.

[nacin]

In 25778:

Account for the possible failure of disk_free_space() in update_core().

see #22704, #25576.

[nacin]

In 25796:

In show_message(), only print error data if it is a string.

see #25576, [25775].

[dd32]

In 25831:

Silence PHP warnings from disk_free_space(). disk_free_space() will produce a warning in error conditions in addition to returning false, this includes a case where the bytes free is greater than PHP_INT_MAX (which is a error condition we don't need to check).
See #25576, #22704