fix proposition for stat.st_dev unsupported (Solaris 32b)

[Aldian-fr]

For reference I came here after investigating https://logstash.jira.com/browse/LOGSTASH-665

It appears that the bug comes from filewatch which can't use stat.st_dev on Solaris. But (see my comment 22253 on the bug report) after replacing occurences of stat.dev_major and stat.dev_minor by nil, the bug disappeared.

I need an indication on the safety risk of this hack since I am not used to ruby, and in case there would not be too much, I suggest you should catch the exception and use nill as a default value.

[Aldian-fr]

I investigated a little more. Traditionally, the usage of dev_major & dev_minor avoid collision between two files from two different disks. But inside filewatch there is a priori no risk of collision because it seems that filewatch always refers to a file by its path. It's mostly guessing, but as far as I understand the code, filewatch uses the inode uniquely in its sincedb file for detecting a rollover, so my proposition could work...

...If there was not another issue that I detected only today: it is similar to https://logstash.jira.com/browse/LOGSTASH-429 that already have a fix been merged but only for windows. After checking every sincedb file that were written since I started experimenting, I finally noticed that the number corresponding to the inode is always 0.

Seems like a quite old bug from ruby...

Since it seems that @edwinf fixed it for windows in #22 I think that next I am going to look into it