options in view change methods, ability to turn on/off animation, closes #1616
rename zoom/panOptions to zoom/pan in setView options
accept global animate option in setView
minor cleanup
accept true as a third setView argument for compatibility
Merge pull request #1642 from gumballhead/master

hasLayer and removeLayer by id.
Merge pull request #1617 from Leaflet/setview-anim

Control animation in setView/panTo/setZoom/fitBounds/etc.
add optional popup argument to Map closePopup
Extend #1642 to include FeatureGroups.
Merge branch 'layers-by-id'