Include URL in bad URL error message, wrap error describing problem

[snasphysicist]

When failing to extract a scheme from a URL, include the URL in the error message. This would make it easier to disambiguate between faulty database URLs and faulty source URLs.

[coveralls]

Pull Request Test Coverage Report for Build 1663268957

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 57.82%

---

Totals
Change from base Build 1595125260:	0.02%
Covered Lines:	3734
Relevant Lines:	6458

---

💛 - Coveralls