identify: document -r. explicitly how to disable wdir scanning (issue5622)

lfs: add a comment to describe subtle local blobstore open() behavior

tests: make #testcase available as env var in test It can be useful for e.g. helper functions to behave differently depending on which test case is being executed. This patch helps with that by making the #testcase case available as a TESTCASE environment variable. Differential Revision: https://phab.mercurial-scm.org/D1816

archive: add support to specify hidden revs if directaccess config is set Differential Revision: https://phab.mercurial-scm.org/D1812