allow Enumerables to be used with "where" filter

Enumerable module responds to `select` so this shouldn't be a problem here. Typical use case would be an object from a plugin being passed through a where filter.
site_template/_includes/head.html: Minor refactoring.

Remove unneeded end tag, and also strip newlines.
Move `X-UA-Compatible` just after `meta charset`.
site_template/feed.xml: Remove unneeded space.
Merge pull request #2980 from tamagokun/patch-1
Update history to reflect merge of #2980 [ci skip]
Revert "Allow Enumerables to be used with "where" filter"
Merge pull request #2985 from jekyll/revert-2980-patch-1

Revert "Allow Enumerables to be used with "where" filter"
Remove reverted #2980 from History.
Merge pull request #2982 from XhmikosR/page-description
Update history to reflect merge of #2982 [ci skip]
Add rbtrace and stackprof and a script/benchmark script.
Link atom feed from html head

This makes it possible for browsers to autodiscover the feed. Fixes https://github.com/jekyll/jekyll/issues/2995
Merge pull request #2993 from jekyll/benchmarking
Update history to reflect merge of #2993 [ci skip]
Move script/benchmark to script/stackprof. [ci skip]
Cache the extname regexp in Converters::Markdown and Textile
Cache variables that won't change through the life of an object
Only compile the Converter#matches regexp when asked for
Add test for Document#basename_without_ext
Only run script/bootstrap in stackprof if stackprof executable isn't there