Log Message:
Update to 1.52

Upstream changes:
1.52    Wed Dec  5 10:00:56 CST 2018
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[ENHANCEMENTS]
click_ok() method can now take a button with X/Y coordinates.
Thanks to GitHub user @marderh.  (GH #45)

Added the ability to modify the HTML that the html_tidy_ok() validates.
See the content_for_validation() method. (GH #61)

Add a set of methods for existence of IDs: id_exists(), id_exists_ok(),
ids_exist_ok(), lacks_id_ok() and lacks_ids_ok(). (GH #48)

Add button_exists(), button_exists_ok() and lacks_button_ok()
methods.  (GH #50)

[FIXES]
Clarified warnings to make it clear that certain modules are
optional. Thanks, Matthew Chae.