Remove stray references to 2.10.2

After this change:

	% ack -l --markdown 2.10.2
	documentation/api.md
	download/_posts/2013-05-31-2.10.2-RC2.md
	download/_posts/2013-06-06-2.10.2.md
	news/_posts/2013-05-23-release-notes-v2.10.2-RC1.md
	news/_posts/2013-05-29-release-notes-v2.11.0-M3.md
	news/_posts/2013-05-31-release-notes-v2.10.2-RC2.md
	news/_posts/2013-06-06-release-notes-v2.10.2.md
	news/_posts/2013-07-11-release-notes-v2.11.0-M4.md
	news/_posts/2013-09-18-release-notes-v2.10.3-RC2.md
	news/_posts/2013-09-24-release-notes-v2.10.3-RC3.md
	news/_posts/2013-10-01-release-notes-v2.10.3.md

	% ack -l --markdown 2.10.3
	documentation/api.md
	download/_posts/2013-09-18-2.10.3-RC2.md
	download/_posts/2013-09-24-2.10.3-RC3.md
	download/_posts/2013-10-01-2.10.3.md
	download/index.md
	news/_posts/2013-09-18-release-notes-v2.10.3-RC2.md
	news/_posts/2013-09-24-release-notes-v2.10.3-RC3.md
	news/_posts/2013-09-28-release-notes-v2.11.0-M5.md
	news/_posts/2013-10-01-release-notes-v2.10.3.md
Reduce duplication of version number in download page sources.

 - add a plugin that provided a liquid filter that expands variables
 - use this in the download pages