Fix default CMAKE_BUILD_TYPE value

[tpadioleau]

Fix default CMAKE_BUILD_TYPE value, fixes #617

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• you have added unit tests for any new or improved feature;
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[tpadioleau]

@benoitmartin88 as discussed, here is the PR

[benoitmartin88]

Looks good. Thanks.

[jbigot]

Looks like a good and needed fix. Thanks

[jbigot]

As soon as all the "administrative" stuff is taken care of (issue, author, etc.) I'd say this is good to ship

[tpadioleau]

As soon as all the "administrative" stuff is taken care of (issue, author, etc.) I'd say this is good to ship

done