ui: indent _writenobuf() to prepare moving bits from _write() functions

ui: simply concatenate messages before applying color labels This should be cheaper in space than applying labels for each message.

ui: simplify interface of low-level write() functions _write() and _write_err() will be replaced with fout.write() and ferr.write() respectively. This is the first step.

ui: factor out function that writes data to fout/ferr with labeling I'm thinking of adding an option to send status messages to stderr (or a dedicated command-server channel) so that structured output (e.g. JSON) would never be interleaved with non-formatter output. A unified write() interface helps to do that.

ui: consolidate places where _progclear() is called The progress bar has to be cleared when we start writing some data to the output stream. Let's make it always triggered immediately before switching by _colormode, so that we can easily factor out helper functions.

templater: compute revset lazily This speeds up e.g. "{ifcontains(rev, revset('::.'), ...)}" in common cases where 'rev' is near the working parent. The templater API is ugly, but it helps here. 'f' can be either a generator or a function returning a generator.

remotefilelog: drop compat code for "getbundle_shallow" wireprotocol command Doing some annotate on hgexperimental shows that getbundle_shallow used to exist in 2013 or before. We don't have any pre-2013 remotefilelog users except Fb themselves and I doubt they are going to use in-core remotefilelog. So it's safe to remove this. Differential Revision: https://phab.mercurial-scm.org/D5193