Add perms test to Qpsmtpd::DB::File::DBM::dir()

[jaredj]

No description provided.

[coveralls]

Coverage increased (+0.05%) to 49.11% when pulling 2740f06 on jaredj:writeable-dir into 573f7c5 on smtpd:master.

[jaredj]

This is ready except for the question of what to do when one of the default 'candidate directory' locations exists but is not writeable. We currently skip such a directory with no warning. It has been suggested to warn on this condition, however because of the (perhaps convoluted) way that we search for valid directories, this could lead to problems:

1. static directories /dir1/ and /dir2/ are being searched
2. /dir1/ has been unwriteable for months, so /dir2/greylist.dbm is being used
3. the admin notices a warning about /dir1/ being unwriteable, and "fixes" it with a chmod
4. the greylist plugin begins ignoring /dir2/greylist.dbm, creating a fresh new database in /dir1/, and suddenly greylisting a bunch of new systems and potentially causing mail flow interruption

[msimerson]

It has been suggested to warn on this condition, however because of the (perhaps convoluted) way that we search for valid directories, this could lead to problems:

Then warn of that possibility. Not warning about existing (possibly used) dirs and letting the sysadmin do something more intelligent than you can automate is likely the type of silent error that's could lead to the scenario you describe.

[jaredj]

I think I can come up with something.

[jaredj]

Something seems to be broken with Coveralls preventing Travis from functioning correctly. This does pass manual travis, though

[coveralls]

Coverage increased (+0.2%) to 49.23% when pulling 88c55ed on jaredj:writeable-dir into 1965006 on smtpd:master.