Fix libevent issue in configure script

[maxim-ky]

Hi guys
There is a problem with "--with-libevent" option in configure.pl. It just doesn't work :)

[mnunberg]

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[mnunberg]

Will be closing this pull request in 1 week if there is no further activity. The patch is OK, but for legal reasons we require you to go through our code review system and sign the CLA.

[maxim-ky]

Okay, I've got it. If you don't mind I'll do it a bit later.

[cb-sdk-robot]

Thanks for the pull request!! To ensure quality review, Couchbase employs a code review system based on Gerrit to manage the workflow of changes in addition to tracking our contributor agreements.

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::SDKBOT/PR:no_cla