Improve parameter sanitization in WP_Date_Query::build_query().

* Don't run non-numeric values through intval() for sanitization; this transforms them into 1s and 0s, which can cause unintended results.
* Be more generous about numeric array keys (don't require 0 and 1) in BETWEEN and NOT BETWEEN clauses.

Fixes #29801.
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git-svn-id: http://core.svn.wordpress.org/trunk@29566 1a063a9b-81f0-0310-95a4-ce76da25c4cd