Fix #13655
Close gh-1209
Ref 32b066d3

(cherry-picked from 26ce2178)

(cherry-picked from 22c515c6)

(cherry-picked from a81dbc4e)

(cherry-picked from 14872941)

It's not easy to find a CSS property that is implemented even in
ancient browsers and that returns a consistent result among browsers
when passed through .css(). color didn't work since Firefox normalizes
it an empty value to rgb(0, 0, 0).

(cherry-picked from 0c12cb39)

Don't require body in the support.boxSizing test.

The workaround to be able to change !important styles broke the browser
keeping the old CSS value if the new one was rejected. Patching it would
involve a significant perf hit (~33%) so the initial patch needs to be
reverted instead.

Tests by m_gol & gibson042.

(cherry-picked from 10e65421)

Fixes #14836
Closes gh-1532

Fixes #14859

Followup to a4b9bc57, #14773

Fixes #14802
(cherry picked from commit 2df1aad6)

Fixes #14792
(cherry picked from commit f4b37d89)

Fixes #14791
(cherry picked from commit 06adf7c9)

Conflicts:
	src/event.js

Fixes #14773
(cherry picked from commit 3a68c114)

Conflicts:
	src/ajax/load.js

Fixes #14179
(cherry picked from commit 10efa1f5)

(cherry-picked from 279913c7)

Fixes #14794

Ref badcd1b6
Closes gh-1518

Ref #14798
Ref gh-1516
Ref gh-1338

Fixes #14798
Close gh-1516
Ref gh-1338

Conflicts:
	bower.json

(cherry-picked from 70ac4485)

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 6d2ab64d)

(cherry-picked from de75b3cc)

Fixes #14785
Ref #13754
Ref badcd1b6

(cherry-picked from 95b21c6e)

(cherry-picked from a74ad04b)

(cherry-picked from cd4e25e9)

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

(cherry-picked from 988d99ad)

Fixes #14717
Closes gh-1496

(cherry-picked from d41fc68d)

(cherry-picked from d63243d0)

This fixes an error introduced by the previous commit.

Fixes #14731