[perl #115818] Don’t croak for /[.zog.]/

[perl #115818] Don’t croak for /[.zog.]/

/[.zog.]/ produces a warning, because the POSIX syntax is not used
correctly.  It must be /[[.zog.]]/.

/[[.zog.]]/ croaks, because that POSIX syntax has not been imple-
mented yet.

There is currently a croak for the former, too, even though it is
the latter syntax that is forbidden.  There is no reason to forbid
the former.

The reason for warning is that /[.zog.]/ is a regular character
class (equivalent to [.zog]), so it might not do what the programmer
intended.  If that is why we warn, it doesn’t make sense to croak.
After all, perl is only guessing that the programmer *might* have made
a mistake.

This makes /[.foo.]/ similar to /[:foo:]/, which warns and then acts
like /[:fo]/.