un-closured curl.js 0.6.3 through 0.6.5 don't get along with Safari 6

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Tiago discovered that un-closured curl.js is failing in Safari 6, which is due to be released imminently.  It seems recent release candidates of Safari 6 fail loudly when attempting to assign a property to a string: `myString.foo = true;`.  Other browsers fail silently.  (There is a line in the config-parsing routine that handles strings and objects generically and so may assign a property to a string.)

Tiago offered a pull request, but we added a temporary fix that is even simpler: remove "use strict", which was added in 0.6.3.  Version 0.6.6 no longer includes "use strict".

**If you are using a closure-compiled version of curl.js, your code is not affected.  All files in the `dist/` folder are unaffected.**

**If you are using packages instead of paths, your code is also unaffected.  This bug only manifests itself when using paths.**

-- J

0.6.6: https://github.com/cujojs/curl

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The good news is that Safari 6 finally fixes broken link.onload and link.onerror event handlers! (new css! plugin that uses those is "in the works" already)

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Just a reminder.  Safari 6 is out today.  If you're using un-compiled curl.js 0.6.3 through 0.6.5, please update to 0.6.6 ASAP.  :)