#### Brief overview of PR changes/additions
A few of Mudlet's files had been accidentally left out of the build
list, and a couple were listed twice. This adds the missing ones,
removes the duplicates, and adds an automatic check that catches this
kind of slip-up from now on.
#### Motivation for adding to Mudlet
When a file is missing from the build list it can quietly cause trouble
for the people working on Mudlet, and in one recent case it contributed
to a feature breaking. The new check makes the problem impossible to
miss, so it gets noticed and fixed before it reaches anyone.
See Also: [Discord
chat](https://discord.com/channels/283581582550237184/283582439002210305/1517465119700029440)
#### Other info (issues closed, discussion etc)
Builds and runs cleanly on macOS; the new check passes and was confirmed
to flag the original missing and duplicated files.
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Signed-off-by: Mike Conley (aka Tamarindo) <sousesider@gmail.com>
Signed-off-by: Michael Conley <sousesider@gmail.com>
