diff: use fctx.isbinary() to test binary The end goal is to avoid calling fctx.data() when unnecessary. For example, if diff.nobinary=1 and files are binary, the expected behavior is to print "Binary file has changed". That could avoid reading fctx.data() sometimes. This is mainly to enable an external LFS extension to skip expensive binary file loading sometimes (read: most of the time with diff.nobinary=1 and diff.text=0), without any behavior changes to mercurial (i.e. whether a file is LFS or not does not change any behavior, LFS could be 100% transparent to users).

pycompat: extract helper to raise exception with traceback It uses "raise excobj, None, tb" form which I think is simpler and more useful than "raise exctype, args, tb".

largefiles: make sure debugstate command is populated before wrapping Copied the hack from 869d660b8669, which seemed the simplest workaround. Perhaps debugcommands.py should have its own commands table.

check-code: ignore re-exports of os.environ in encoding.py These are valid uses of os.environ.