Added support for no timeout locks on db files

[dmoklaf]

Currently the bolt library supports timeouts for db file locking, as well as infinite timeouts. This patch adds support for no timeouts at all.

[dmoklaf]

Hello is there any problem with this patch, or required updates?
Thanks

[benbjohnson]

@rgeronimi Sorry, I'm just terrible at managing PRs. Can you add a test for this change? Otherwise it lgtm.

[dmoklaf]

Is ok, I thought there was a code reason :)
I will take some time to add a few tests and I come back to you.
Have a nice Xmas

[dmoklaf]

Hello, I freed up the time to add the missing test. Unfortunately I was about to add a variant of the exact piece of code removed through
commit b9eb643
(@benbjohnson committed on 27 Dec 2016 )
"The new FCTNL locking does not support multiple locks from the
same process which makes those tests fail. The lock tests have
been removed."

I see 2 alternatives:

• In line with this commit we drop entirely the objective to test lock-related functionality
• We use fork a side process to hold the commit

Unfortunately the second alternative requires an external executable (Fork and not ForkExec is not safe to call from within a Go process, as it forgets about Go runtime-related threads in the forked process) which is, depending on how and when tests are run, not trivial.

Should I continue down that second alternative? If yes, I need a separate Go executable which will need to be go-built before the go-test stage begins. Do you see any simpler approach than that?

Thanks