Return an empty object instead of null for non-specifiec `parameters` in LoaderInfo

This doesn't add support for actually supplying parameters, so it's mostly a stub.
Properly clamp values or throw errors in some Stage setters

assert mustn't ever be used on content-supplied values.
Merge pull request #1452 from tschneidereit/nat

Bugfixes in Stage and LoaderInfo builtins
Fixes Stage.align setter.
Stage.align setter test.
Bug 1037541 - Implement AVM2 opcode astype (0x86)
Merge pull request #1454 from tschneidereit/avm2-ops

Bug 1037541 - Implement AVM2 opcode astype (0x86)
Bug 1037541 - Follow-up for stupid error in supposedly-safe last-minute change
Merge pull request #1455 from tschneidereit/avm2-ops

Bug 1037541 - Follow-up for stupid error in supposedly-safe last-minute change
Bugfix in describeTypeJSON's addTraits function
Bind stubs for GameInput-related classes in the natives linker

Needed for the "The Sea Has No Claim" game.
Bind stubs for Multitouch-related classes in the natives linker

Needed for the "The Sea Has No Claim" game.
Merge pull request #1456 from tschneidereit/nat

Bugfixes for "The Sea Has No Claim" game
Change TextField#gridFitType accessor to non-throwing stub
Merge pull request #1457 from tschneidereit/nat

Change TextField#gridFitType accessor to non-throwing stub
Fixes references in AVM2 shell so that tests pass again.
Merge.
Merge.
Merge pull request #1458 from mbebenita/nat

Fix stage align settter and make shell tests pass again.
Some assertions.