Introduces txp:authors tag.

This tag can be used to render author lists.

Closes issue #369

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5328 2fea6a4d-a838-0410-917b-93a53c48e9d2
Should be $realname.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5329 2fea6a4d-a838-0410-917b-93a53c48e9d2
in_list() compares values strictly as strings.

Prevents type juggling side-effects.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5330 2fea6a4d-a838-0410-917b-93a53c48e9d2
txp:if_author and txp:if_article_author check as strings.

Sweeping the codebase and removing any error-prone
conditionals.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5331 2fea6a4d-a838-0410-917b-93a53c48e9d2
Fix form and contained statement checks.

Number of tags would ignore 'empty' contained statements.
As longs as it's set, it's set and should be used. Even an
empty string or a zero is a valid statement and shouldn't
be silently ignored.

Same goes for forms. Eventually we will have support for
zeros as the name for any content, including categories,
links, authors, pages and forms.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5332 2fea6a4d-a838-0410-917b-93a53c48e9d2
Merge remote-tracking branch 'upstream/master'