Fish Trophy

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Don't check for hg executable if we're using hgweb.

Review Request #1111 — Created March 6, 2018 and updated

Review Board
If a Review Board instance uses hgweb for all communication with Mercurial
repositories, it is not necessary to have a hg executable on that system.

Testing Done:
Removed hg executable from system and saw that a diff can be shown und a new
review request could be opened by post-commit /r/new/

Reviewed at