fix #950, find with falsy values should returns empty array
Added windows phone detection
Added $.os.wp to tests, and fixed ie conditional
Merge pull request #961 from haas85/master

Added windows phone detection
Merge pull request #959 from hojs/find-with-falsy

Find with falsy values should returns empty array
Fix confusion of `.attr('value')` and `.val()` on `<input>`

`.attr('value')` should not use `.val()` on `<input>` specially.
Fixes #939

Adds `testValVsValueAttr` to confirm their relations.