Updating the master version to 2.1.1pre.
Build: Upgrade npm devDependencies
Build: Remove obsolete UglifyJS workaround
Tests: Blacklist beforeunload test in iOS

iOS has the window.onbeforeunload field but doesn't support the beforeunload
handler making it impossible to feature-detect the support.

Fixes #14717
Closes gh-1496
Support: Add iOS6 support tests results
Build: Specify browserSets for TestSwarm directly
Ajax: Protect against exceptions thrown synchronously by xhr.send

When xhr.send throws an exception synchronously, the onerror handler may have
been called already which, unchecked, makes the exception bubble up outside of
jQuery.ajax.

We now catch the exception pre-emptively and only rethrow if we know it hasn't
already been notified through the onerror handler.

Fixes #14683
Core: Remove special case try/catch in isPlainObject

Fixes #14746
Build: Switch to explicit dependencies versions in bower.json
Attrs: Simplify an option hook

Since getter was removed in fdd78fad19ea3390cd96971cd29430e36378d137
there is no longer a need to wrap option element in order to get its value

Fixes #14756
Selector: update Sizzle
Build: Upgrade QUnit to 1.14.0
Docs: Change raises to throws in README test assertions
Support: Document box-sizing was unprefixed in Firefox 29
Tests: remove all the empty line whitespace