Browser-like treatment of whitespace in text

HTML content usually spans multiple lines, with linebreaks and whitespaces
being insignificant. However, `text?`, `regex?`, `some-text?`, `some-regex?`
apply their validations rigidly. As such, these tests are fragile -- for
instance, if someone changes the template file of the underlying content, the
tests may fail.

With this changeset, the aforementioned tests now replace all one or more
consecutive whitespace characters (i.e., ' ', '\t', '\n', etc.) in the text of
the page/element with a single space.  This feature allows the tests to ignore
line breaks and spacing issues in the source text, and thus, making the tests
more robust.