largefiles: avoid dynamically subclassing context instances E.g. copies.pathcopies() compares context objects for equality and basectx.__eq__ compares the type. But since largefiles was dynamically creating classes, they would all be unequal. That led pathcopies(), after some changes I made, to not short-circuit to get copy info only from the dirstate. This patch fixes that short-circuiting (and other places where context are being compared for equality). Differential Revision: https://phab.mercurial-scm.org/D7143

relnotes: copy "next" to "5.2" and clear "next" This is the same thing as we did for 5.1 in cba59b338976 (relnotes: copy "next" to "5.1" and clear "next", 2019-08-01). Differential Revision: https://phab.mercurial-scm.org/D7231

py3: avoid `b'%s' % type(...)` in a ProgrammingError Differential Revision: https://phab.mercurial-scm.org/D7363

largefiles: delete unused repo.status_nolfiles() Differential Revision: https://phab.mercurial-scm.org/D7142

largefiles: use context manager for wlock in repo.status() override Differential Revision: https://phab.mercurial-scm.org/D7141

largefiles: allow "lfstatus" context manager to set value to False Differential Revision: https://phab.mercurial-scm.org/D7140