blocking-sessions fix

[rstribrn]

I found out that blocking-sessions mode doesn't really detect blocking sessions! It simply prints "OK - " and returns OK state.
Developed & tested against real Oracle DB and simulated blocking sessions state.

Also introduced support for warning/critical levels (with 10/50 default).

Thanks in advance for merging ;-)

[rstribrn]

Hi Gerhard,
any chance for merging this pull request? ;-)

Thanks in advance
Rostislav

[rstribrn]

Hi,
I used my master branch for creating this pull request (expecting it would be merged in reasonable time). My fault.
As a consequence, when I merged 3.3.2.1 changes into my master, those appeared also as part of this pull request.

Since your (lausser's) master branch doesn't contain released 3.3.2.1 changes, these appear as new commits, but are 1:1 from your 3.3.2.1 tag.

Just FYI.