Avatar alt isn't attribute-escaped, nor translated

[nbachiyski]

In [8661] the avatar alt default value is Avatar and cannot be translated.

Also, if the avatar alt contains ' or tags, it will break the HTML code.

(In [9076]) Avatar alt fixes from nbachiyski. fixes #7536

Giving every avatar a default alt text of "avatar" is very bad accesibility, I can't imagine anything more annoying to a screen reader.

​http://en.wikipedia.org/wiki/Alt_attribute

"While the use of meaningful alt text is necessary to comply with accessibility standards, and is good practice, sometimes an image is used for purely decorative purposes. In this case, one should use an empty alt attribute (alt="")."

Replying to matt:

Giving every avatar a default alt text of "avatar" is very bad accesibility, I can't imagine anything more annoying to a screen reader.

Agree.

Although I introduced this for #7523 I agree with matt here that the default should be empty.

Having a page full of Avatars being read out would get a little frustrating when viewing comments.

(In [9127]) Default to an empty alt attribute on Avatars. Fixes #7536.

Change phpdoc to say that the default is blank

The phpdoc text needs to be changed to say the default is blank.

(In [9200]) get_avatar() phpdoc update from Speedboxer. fixes #7536