Force stop model database cache update

[osrf-migration]

Original report (archived issue) by Nate Koenig (Bitbucket: Nathan Koenig).

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The model database cache update can take a bit of time. If gazebo is quite while it's updating, the shutdown hangs until libcurl completes.

This should be improved by using curl_multi: http://curl.haxx.se/libcurl/c/libcurl-multi.html

[osrf-migration]

Original comment by Nate Koenig (Bitbucket: Nathan Koenig).

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• changed state from "new" to "on hold"

Until 2.0

[osrf-migration]

Original comment by Ian Chen (Bitbucket: Ian Chen, GitHub: iche033).

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• changed state from "on hold" to "open"

[osrf-migration]

Original comment by Nate Koenig (Bitbucket: Nathan Koenig).

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• set version to "all"

[osrf-migration]

Original comment by Nate Koenig (Bitbucket: Nathan Koenig).

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• changed state from "open" to "new"