hgweb: allow defining Server response header for HTTP server By default, the string contains the Python version. Server operators may want to change this. Because we like deterministic tests, we change the test harness to always set this value to a known string. Various globs over the server header have now been removed. # no-check-commit because we add version_string() Differential Revision: https://phab.mercurial-scm.org/D2840

tests: use $HTTP_DATE$ for Date header Support for the $HTTP_DATE$ substitution was recently added. Let's adopt it more widely. We had to tweak the substitution to be case insensitive, since HTTP headers are case insensitive. I also found a minor test issue not globbing over the length of the Server response header. Differential Revision: https://phab.mercurial-scm.org/D2839

debugcommands: introduce actions to perform deterministic reads "readavailable" is useful as a debugging device to see what data is available on a pipe. But the mechanism isn't deterministic because what's available on a pipe is highly conditional on timing, system load, OS behavior, etc. This makes it not suitable for tests. We introduce "ereadline," "read," and "eread" for performing deterministic I/O operations (at least on blocking file descriptors). We stop short of converting existing consumers of "readavailable" in tests because we're working out race conditions and deadlocks on Windows. But the goal is to eventually move tests away from "readavailable" to these new APIs. Differential Revision: https://phab.mercurial-scm.org/D2720