target argument of MovieClipLoader#loadClip and unloadClip may be level

According to the document[1,2], "target" argument of these methods may
be number (level).

[1]: http://help.adobe.com/en_US/AS2LCR/Flash_10.0/help.html?content=00001381.html
[2]: http://help.adobe.com/en_US/AS2LCR/Flash_10.0/help.html?content=00001389.html
Regenerate avm1lib (#763)
Merge branch 'master' into loadClip

Conflicts:
	src/avm2/generated/avm1lib/avm1lib.abc
Merge pull request #838 from yurydelendik/loadClip

Load clip fixes for AVM1