Wrap imagejpeg et al to support stream wrappers

[adambackstrom]

The GD functions imagejpeg(), imagegif() and imagepng() do not support writing to PHP stream wrappers. This patch provides new wp_imagejpeg(), wp_imagegif(), and wp_imagepng() functions which wrap the GD functions, and a backend function _wp_imageany() which (if necessary) output buffers the image and writes to a stream URL.

A supporting function, wp_is_stream(), is used to identify paths that are stream URLs.

An alternative implementation of _wp_imageany() could write the image to a tmpfile and then copy the image to the stream URL.

[adambackstrom]

gd-imagejpeg-wrapper-ob.2.diff is a dupe, please ignore.

[adambackstrom]

Alternate using temp file rather than output buffering (recommended by dd32)

[adambackstrom]

Bugfix output buffered version; always turn off ob before function ends (thanks, dd32)

[adambackstrom]

Prevent wp_mkdir_p from stripping after the URL scheme

[adambackstrom]

Prevent wp_mkdir_p from stripping // after the URL scheme

[nacin]

I would really like to see this added to 3.5, to complement our focus on the media, upload, and gallery user experience.

I think this is closely related to #6821.

[markoheijnen]

Fixed in [22094]