merge with stable

demandimport: support importing builtins for Python 3 __builtin__ was renamed to builtins in Python 3. If importing __builtin__ fails, fall back to importing builtins in order to support Python 3.

demandimport: alias __builtin__ as builtins Python 3 renamed the __builtin__ module to builtins. In preparation for supporting Python 3, alias the imported module as "builtins."

bufferedinputpipe: remove N^2 computation of buffer length (issue4735) The assumption that dynamically computing the length of the buffer was N^2, but negligible because fast was False. So we drop the dynamic computation and manually keep track of the buffer length.

bufferedinputpipe: remove an outdate comment This comment is the remains of a intermediate implementation using self._buffer += data This implementation never made it to the repository and we can safely drop the comment.

statichttprepo: kill off sopener

obsolete: replace references to 'sopener' with 'svfs'

exchange: replace references to 'sopener' with 'svfs'

localrepo: kill off sopener (API) sopener is deprecated since 7034365089bf (Mercurial 2.3). It's annoying for extension authors to have to deal with both. Let's just kill it off.

share: replace reference to 'sopener' with 'svfs' sopener is deprecated. It's annoying for extension authors to have to deal with both. Let's just kill it off.