Some clean-up of how we handle unrecognized annotation
- add a flag extra_annotation_name
- tie unknown annotation warnings to --warning_level rather
than --compilation_level
- add annotations from jsdoc3 to the default set.
fixes issue 901

R=blickly
DELTA=77 (63 added, 12 deleted, 2 changed)


Revision created by MOE tool push_codebase.
MOE_MIGRATION=6185


git-svn-id: http://closure-compiler.googlecode.com/svn/trunk@2485 b0f006be-c8cd-11de-a2e8-8d36a3108c74