Prevent moodle_url error, cleanup entity encoding and decoding, disable tex source view when TeX and Algebra plugins disabled, localise TeX source popup and prevent phishing attempts, fix executable permission of Algebra pearl script, prevent image error in tex debug when Tex/Ghostscript not configured properly, fix copyright blocks and phpdocs, improve coding style, fix wrong source display link in Algebra filter.
It seems some TeX installs use a convert utility that renders poor quality
images when using the GIF format, but render good ones when using PNG. If
all the needed tools are available, let the admin choose the preferred
output format.
Merged from MOODLE_19_STABLE
Petr Skoda