Core Updates: Verify that all files we're about to copy are actually writable, when using the direct transport.

Once we begin to copy core files, all bets are off. This allows us to fail early when we'll otherwise need to stop midway through due to permissions issues, which is a particularly bad problem when only some files have permissions issues.

see #22704.

Built from https://develop.svn.wordpress.org/trunk@25794


git-svn-id: http://core.svn.wordpress.org/trunk@25706 1a063a9b-81f0-0310-95a4-ce76da25c4cd
3.7-beta2-25795

Built from https://develop.svn.wordpress.org/trunk@25795


git-svn-id: http://core.svn.wordpress.org/trunk@25707 1a063a9b-81f0-0310-95a4-ce76da25c4cd
In show_message(), only print error data if it is a string.

see #25576, [25775].

Built from https://develop.svn.wordpress.org/trunk@25796


git-svn-id: http://core.svn.wordpress.org/trunk@25708 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Only add error data to the files_not_writable WP_Error if the install already has [25775] and [25796] applied.

see #22704.

Built from https://develop.svn.wordpress.org/trunk@25797


git-svn-id: http://core.svn.wordpress.org/trunk@25709 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Avoid our pre-flight writable checks if get_core_checksums() doesn't exist yet.

Thus, it will not work for 3.6 => 3.7, only 3.7+.

see #22704.

Built from https://develop.svn.wordpress.org/trunk@25798


git-svn-id: http://core.svn.wordpress.org/trunk@25710 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove accidental debug cruft in [25780]. see #22704.

Built from https://develop.svn.wordpress.org/trunk@25799


git-svn-id: http://core.svn.wordpress.org/trunk@25711 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use correct variable. see #22704.

Built from https://develop.svn.wordpress.org/trunk@25800


git-svn-id: http://core.svn.wordpress.org/trunk@25712 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Significantly simplify get_core_checksums(), as the caching and chunking was causing too much grief.

Make sure we only do our pre-flight is_writable check when the file exists.

see #18201. see #22704.

Built from https://develop.svn.wordpress.org/trunk@25801


git-svn-id: http://core.svn.wordpress.org/trunk@25713 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: better logic for featured image HTML output, and add fallback message for focusable anchor elements, for accessibility. Fixes #25325.
Built from https://develop.svn.wordpress.org/trunk@25802


git-svn-id: http://core.svn.wordpress.org/trunk@25714 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: link hover improvements, props sabreuse. See #25054.
Built from https://develop.svn.wordpress.org/trunk@25803


git-svn-id: http://core.svn.wordpress.org/trunk@25715 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: remove excerpts from featured posts, and display full titles instead. Props iamtakashi, closes #25581.
Built from https://develop.svn.wordpress.org/trunk@25804


git-svn-id: http://core.svn.wordpress.org/trunk@25716 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Avoid numerous potential PHP warnings when dealing with the pre-r25801 get_core_checksums() return value.

Warnings included current(), filestat(), and md5_file().

see #18201. see #22704.

Built from https://develop.svn.wordpress.org/trunk@25805


git-svn-id: http://core.svn.wordpress.org/trunk@25717 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Language Packs: Many many fixes such as:
- Add a "Update Translations" stand-alone button to the updates page
- Shift Language feedback to before update process completion action links & limit the verbosity of output (name + success/errors)
- Simplify/combine the language update descriptive string to only include a plugin/theme name
- Properly handle cache clearing after language updates to prevent langs being repeditively updated
- Display a "All items up to date" string when there's nothing to do
- Reduce the 'Connection Information' from a <h2> to a <h3> to remove duplicate h2's and screen icons from update screens
- Fix the Direct filesystem method not being used for Language updates because WP_LANG_DIR doesn't exist (check it's parent for writable instead)
See #18200, #22704


Built from https://develop.svn.wordpress.org/trunk@25806


git-svn-id: http://core.svn.wordpress.org/trunk@25718 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove the no longer used Headerless_Upgrader_Skin class, it's been replaced by Language_Pack_Upgrader_Skin.
See #18200, [25806]

Built from https://develop.svn.wordpress.org/trunk@25807


git-svn-id: http://core.svn.wordpress.org/trunk@25719 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: first pass at implementing Featured Content settings, props obenland. See #25549.
Built from https://develop.svn.wordpress.org/trunk@25808


git-svn-id: http://core.svn.wordpress.org/trunk@25720 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Avoid printing a possible HTML element. fixes #24813.

Built from https://develop.svn.wordpress.org/trunk@25809


git-svn-id: http://core.svn.wordpress.org/trunk@25721 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Include translations in the update bubbles (as +1 if there are any). see #18200.

Built from https://develop.svn.wordpress.org/trunk@25810


git-svn-id: http://core.svn.wordpress.org/trunk@25722 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Avoid a few PHP Warnings when files don't exist and use a better method to locate the local filepath.
See #18201

Built from https://develop.svn.wordpress.org/trunk@25811


git-svn-id: http://core.svn.wordpress.org/trunk@25723 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix a issue where the translation name isn't showing up in the Background Update emails, caused by a PHP Warning/missing variable in [25806]. See #18200

Built from https://develop.svn.wordpress.org/trunk@25812


git-svn-id: http://core.svn.wordpress.org/trunk@25724 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: implement tag auto-complete for featured content settings, and uppercase `__CLASS__` for consistency. Props kovshenin, see #25549.
Built from https://develop.svn.wordpress.org/trunk@25813


git-svn-id: http://core.svn.wordpress.org/trunk@25725 1a063a9b-81f0-0310-95a4-ce76da25c4cd