buffer: construct new buffer from buffer toJSON() output

Creating a new buffer from the toJSON() output of another
buffer does not currently work. This commit adds that
support. Closes #7849.

Signed-off-by: Fedor Indutny <fedor@indutny.com>
node: fix #7841 by overlooking the spare sourceline

Signed-off-by: Fedor Indutny <fedor@indutny.com>
http: remove unused code block

fix #7769

Signed-off-by: Fedor Indutny <fedor@indutny.com>