Css: Don’t cache support.reliableMarginRight; thanks @jdalton, @timmywil

Fixes #14731
Css: Fix the reliableMarginRight test in oldIE.

This fixes an error introduced by the previous commit.
Build: Upgrade npm devDependencies

(cherry-picked from d63243d085c797e53a965620c439277284eada59)
Build: Remove obsolete UglifyJS workaround

(cherry-picked from d41fc68d9b89d39f8c71ae9f810b72798ff3e9ac)
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.

(cherry-picked from 988d99ad278c2c9dc16c68f86bddc4df99dcd928)

Fixes #14717
Closes gh-1496
Css: Document reliableMarginRight is needed for Android 2.3
Support: Add iOS6 support tests results
Build: Specify browserSets for TestSwarm directly
Build: Switch to explicit dependencies versions in bower.json

(cherry-picked from cd4e25e991898bf07ce82fe4ab3d60c32b4a5fc9)
Selector: update Sizzle

(cherry-picked from a74ad04bc9c4c7203303b2547e94f1cc53c2a460)
Build: Upgrade QUnit to 1.14.0

(cherry-picked from 95b21c6ec2790d0d051cdfe95d73148d7c385d68)
Docs: Add support comments for prefixed box-sizing
Docs: Remove the note about consequences of excluding Sizzle from README
Core: Correct support comments for String.prototype.trim
Support: Skip style-based tests when element.style is undefined

Fixes #14785
Ref #13754
Ref badcd1b6f301e6253405f17759c1270549a34e12
Css: Don't check fill-opacity in Android 2.3, it's not supported

(cherry-picked from de75b3cc626829c3478a8a6d59dddc948d348b41)
Event: Blacklist the onbeforeunload test in Android 2.3

Similarly to iOS, Android 2.3 has the onbeforeunload property on window
but doesn't support the event. This commit blacklists the test there as well.

(cherry-picked from 6d2ab64df7bdda087e79deaa53db969fa6f2cd92)
Effects: Don't check fill-opacity in Android 2.3, it's not supported

(cherry-picked from 70ac4485f30633074696fa28ca29b0325459f228)