hugolib: Sync page collections with Site.Info on rebuild in watch mode
hugolib: Sync page collections with Site.Info on rebuild in watch mode

There is definitive potential for cleanup in this area, but this will have to do for now.

Fixes #2869

anthonyfok/hugo,mdhender/hugo,fedelibre/hugo,digitalcraftsman/hugo,fedelibre/hugo,MarkDBlackwell/hugo,mitchchn/hugo,gohugoio/hugo,gohugoio/hugo,tubo028/hugo,mdhender/hugo,tubo028/hugo,fedelibre/hugo,mdhender/hugo,gohugoio/hugo,anthonyfok/hugo,anthonyfok/hugo,digitalcraftsman/hugo,mitchchn/hugo,fedelibre/hugo,mdhender/hugo,MarkDBlackwell/hugo