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Update files for 1.7.4.
Update docs/Release.txt.
Set MPC_NIGHTLY_RELEASE to 1.
WebUI: Cleanup.
WebUI: only make available to global scope the functions we need to access.
Use AtlEscapeUrl/AtlUnescapeUrl to do URL encoding/decoding.

This is now available outside of ATL Server. It avoids using our incomplete URL encoding function.