Fix alert-exceeds-max feature for files > 2GB and < max-filesize

[val-ms]

The --alert-exceeds-max feature should alert for all files larger than 2GB because 2GB is the internal limit for individual files. This isn't working correctly because the goto done; exit condition after recording the exceeds-max heuristic skips over the logic that reports the alert.

This fix moves the ">2GB" check up to the location where the max-filesize engine option is set by clamd or clamscan. If max-filesize > 2GB - 1 is requested, then max-filesize is set to 2GB - 1.

Additionally, a warning is printed if max-filesize > 2GB is requested (with an exception for when it's maxed out by setting --max-filesize=0).

Resolves: #1030

[val-ms]

Note: I'm actually a little bit on the fence about the warning when setting max-filesize > 2GB. I expect it will draw a lot of attention. However, a lot of people mistakenly think the limit is 4GB or even unlimited because there is presently no warning.

[ragusaa]

Note: I'm actually a little bit on the fence about the warning when setting max-filesize > 2GB. I expect it will draw a lot of attention. However, a lot of people mistakenly think the limit is 4GB or even unlimited because there is presently no warning.

I like having a warning that a file is not being scanned due to a size limit, so that the user is aware.