Add AtLeastOnce() method

[duskhacker]

Allows a test to ensure that a call happens at least
one time, but doesn't care how many more times a call occurs.

I've added this because in some event-driven testing that I'm doing
I cannot always know how many times the event will happen, so
Times() is not appropriate, but I need to ensure it gets called,
so AnyTimes() is also not appropriate.

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[duskhacker]

I signed it!

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.

[duskhacker]

I signed it!

[duskhacker]

I signed it!

[dsymonds]

This might be better named as MinTimes, and have it only set the minimum. Then there can be a MaxTimes to mirror it.

[dsymonds]

The CLA checker is getting confused. Rackspace has signed a corp CLA, so you're fine on that front.

[duskhacker]

Closing to get this CLA business sorted out.

[duskhacker]

@dsymonds RE CLA: I closed it before I noticed your comment about it. So, I'm confused, can I just ignore that CLA business, or what do I have to do something to make the CLA checker happy?

RE Mintimes/Maxtimes: I'll change it in another branch.

[dsymonds]

Yes, ignore the googlebot complaining about the CLA. I thought it was meant to cope with corporate CLAs, but it clearly isn't in this case. Your contribution is covered by Rackspace's CLA.

[duskhacker]

@dsymonds Thank you for your prompt response! I'll close this and open another one with the changes you suggested.

[dsymonds]

Okay, or you can just amend the commit on this PR. Up to you.