Protect ZoomBox from division by zero

When the map is at the highest zoom level, the old and the current
resolution will be the same. This would cause a division by zero, which
the JavaScript engine does not recognize as such. So we have to protect
zoomOriginPx from becoming {x: Infinity, y: Infinity}.
Merge pull request #996 from ahocevar/zoombox-infinity

Protect ZoomBox from division by zero (r=@marcjansen)
Drag interval of 0 (i.e. no separate cycle) seems appropriate now

The reason for setting this to 1 was ancient IPhones with ancient iOS
versions. On all other devices, 0 seems to work better, and it removes the
overhead of spawning a separate cycle for each drag.
enable TileManager by default as susggested by @marcjansen and @bartvde and discussed with @ahocevar just now
fix up tests
fix up the failing tests
Merge pull request #991 from ahocevar/drag-interval

Kinetic dragging causes multiple requests and hangs an application. r=@bartvde
incorporate @ahocevar's review
Merge pull request #998 from bartvde/tilemgrdefault

enable TileManager by default as suggested by @marcjansen and @bartvde ... (r=@ahocevar)
TileManager dependency management

If the build does not contain TileManager.js, do not create a TileManager
instance for the map. If the build does not contain Layer/Grid.js, do not
try to add Grid layer instances to the list of layers managed by the
TileManager.
Merge pull request #1000 from ahocevar/tilemanager-deps

Dev examples doesn't work
Fixing dependencies

This avoids undefined this.tileManager.addMap, and re-adds the TileManager
to the mobile build profile.
Merge pull request #1002 from ahocevar/tilemanager-mobile

Fixing dependencies. r=@bartvde
Revert "Merge pull request #708 from mpriour/displayEvent"

This reverts commit 0b3f582e1030b9e9211e6098799fcdf9bd3e1ab1, reversing
changes made to 74103ec3e017c8c66ee3ae8f0a7c891c2a2cdd86.

The reason for reverting this is a regression. See #997.
Whenever we run tests *with* the tileManager, we cannot inspect any grid/tiles related things, because all these get asynchronous, so don't use tileManager in all the tests
Merge pull request #997 from ahocevar/revert-708

LayerSwitcher doesnt switch layer entry correctly if Layer is not visible. r=@bartvde
there were 2 more failing tests, do not include tileManager there as well
make iframe visible in TileManager tests so that they pass in FF as well
Merge pull request #1003 from openlayers/notilemgrtest

Whenever we run tests *with* the tileManager, we cannot inspect any grid...(r=@ahocevar)
Don't be able to double activate ModifyFeature Control