commands: add value for cmdtype argument for read only commands In the previous release we added an argument `cmdtype` to registrar.command() which is a enum and tells whether the command is read only, recoverable write or unrecoverable write command. This patch add the value of cmdtype argument for commands which are read only. Differential Revision: https://phab.mercurial-scm.org/D1468

error: add InMemoryMergeConflictsError We'll raise this exception in the merge code, and in-memory users like rebase can catch it and retry without IMM. Differential Revision: https://phab.mercurial-scm.org/D1210

lfs: generate a large file by using `python` instead of yes | head yes(1) on some systems (like gcc112) feels compelled to inform you of broken pipes, such as those triggered by head(1). This works around the problem portably.