Provide way for users to silence warning about detecting changed files

SCR now checks mtime, uid, gid, and mode bits when deleting a file from cache, comparing those to the values it recorded for the file when the application called complete_output. If there is a change, SCR prints a warning for each file.

The point of this is to help the user detect buggy usage of the SCR API, since SCR does not capture any changes to a file after the application has called complete_checkpoint. It likely means the application called complete_output too soon.

However, there might be cases where the user needs to modify files in someway and doesn't care that SCR will miss those particular changes. In this case, the user will get lots of annoying warnings printed. We need a way to shut those off.

Some ideas:

• add a parameter to explicitly enable and report debug checks like this (leaning toward this option)
• add a parameter to explicitly disable those check-on-delete warnings
• only print the warnings when using SCR_DEBUG=1 or higher (this by itself is likely not sufficient, since the user may want SCR_DEBUG output and still want to silence those particular warnings)

None of these are difficult to add. Just creating the issue so I don't forget that we need to do it.