MimeMagic: Don't seek before BOF

This has weird side effects like only extracting the tail of the
file partially or not at all.

Cherry-picked from d96c6f01479ef

Bug: 66428
Change-Id: I182128c6958244f1515227ee742c3206a7484aee
Some corrections to RELEASE-NOTES-1.23

* Fixed a typo: "When $wgJobRunRate is higher that zero [...]".
* Removed a reference to 1.22: "[...] not yet queried but will be
  in a future point release of 1.22."
* Fixed misspellings "wiki's" and "sql" in the same note.

Change-Id: I5fee88c459345ecd8b71f9e5b86c65afae183ba1
filebackend: Avoid using popen() when "parallelize" is disabled

Bug: 66467
Change-Id: Iaf8eb2ecfad166e26e265a98933399dc4bc255a3
Don't allow some E_NOTICE messages to end up in the LocalSettings.php

There is probably a better, more comprehensive way to produce a
LocalSettings.php file so that E_STRICT and E_NOTICE errors don't end
up in the file, or to notify users that there is a problem with the
generated file, at least.   This only attempts to address those issues
reported as a result of c978cee8562f018dab158b41e15266fcf873bf1b.

Bug: 66922
Change-Id: I0fe70446d9fe23aed2a147e20e5ff3851371726d
Special:Watchlist: Don't try to render empty row

If no rows to render in table, show message and leave function before
try to render.

Bug: 67025
Change-Id: Ica4ad670a130f31124ff644a2e1e50beea481c9b
Merge "MimeMagic: Don't seek before BOF" into REL1_23
SECURITY: Prevent external resources in SVG files

On bug 65724, it was discovered that a user could upload SVG images
with embedded <image> elements that pulled in the resource via http.
This could allow an attacker to track all viewers of an SVG by having
the image embed another image hosted on their own server.

While testing the patch, I also identified 3 more element namespaces
that have been used on commons and seem harmless, so I added those to
the whitelist.

Change-Id: Iacc5d3d6248b73740510ba579be9484f4964ca13
Updated release notes and version number to 1.23.1

This is MediaWiki 1.23.1 security and maintenance release.

Change-Id: I66d92d53262f54699c8d4c43434481eb328d8e18
Merge branch 'REL1_23' of https://github.com/wikimedia/mediawiki-core into REL1_23