Locating element by partial text only considers direct child text nodes

[jkotests]

Fixes #866

Note that in the SelectorBuilder::XPath that :text and :contains_text are now the same - ie comparing to normalize-space(). From what I could see, there's no reason that they should ever be different. However, for now, to minimize changes, I have left them separate.

[coveralls]

Pull Request Test Coverage Report for Build 2003

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.439%

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Totals
Change from base Build 2002:	0.0%
Covered Lines:	2321
Relevant Lines:	2382

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 2003

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.439%

---

Totals
Change from base Build 2002:	0.0%
Covered Lines:	2321
Relevant Lines:	2382

---

💛 - Coveralls