move _.before gc conditional to a single line
check for array length when evaluating isSorted
removed tabs to conform with coding style
Merge pull request #1917 from tjbarber/avoid-returning-zero-truthy-isSorted

Fixes #1870: _.indexOf with `isSorted` of `true` will incorrectly match `undefined` on an empty array.
Added _.propertyOf method and tests
Used function(){} in place of _.noop
Merge pull request #1921 from bathos/master

Added _.propertyOf method
Add _.keysIn method