hidden: Add ``hidden`` method for context

hidden: Add a hiddenrevs attributes to changelog. This attributes hold the set of all revisions that should be ommited by command and tools displaying changesets. This set is given as a hit. Command and tools are responsible to check it in order to filter they outpur. Code adding revisions to the set are responsible to the consistency of it's data.

config: handle comment lines in continuations (issue2854)

http: report unexpected unparsable push responses (issue2777)

dispatch: write shell alias output to ui out descriptor

commands: use ui descriptors when reading/writing from stdin/out

cmdutil: return a dummy, closable file object if it cannot be duped If the ui I/O descriptors aren't real descriptors, they cannot be duped. Instead, we return a wrapper object that behaves the same, and can be closed (by overriding close and doing nothing).

cmdutil: use ui descriptors in makefileobj

mq: use ui.fin when importing patch from '-'

cmdutil, logmessage: use ui.fin when reading from '-'