convert: use bytes for value in extra dict The keys and values of the extra dict are expected to be bytes. Before this fix, there was a crash in mercurial.changelog.encodeextra().

archival: abort if compression method is unavailable `tarfile.CompressionError` is documented to be the "exception for unavailable compression methods". Also, make tests conditional on whether the lzma module is available or not.

demandimport: ignore `lzma` module for demandimport This makes importing the module fail if the `_lzma` module is not present. This makes e.g. tarfile correctly recognize if LZMA support is not present. It changes the exception File "/usr/lib/python3.6/tarfile.py", line 1694, in xzopen fileobj = lzma.LZMAFile(fileobj or name, mode, preset=preset) AttributeError: module 'lzma' has no attribute 'LZMAFile' to the more correct exception File "/usr/lib/python3.6/tarfile.py", line 1692, in xzopen raise CompressionError("lzma module is not available") tarfile.CompressionError: lzma module is not available Also, it prevents that the error "abort: No module named '_lzma'!" is shown when a development warning is to be shown. The reason why that happened is that for showing the warning, we get information about the stack frames from the inspect module, which accesses the `__file__` attribute of all modules in `sys.modules` to build some cache, causing all modules (including `lzma`) to be imported.

py3: fix crash when server address is 0.0.0.0 (issue6362) `socket.getfqdn()` assumes that the name is passed as `str` on Python 3 and always returns `str` in this case. Mercurial passed `bytes` (but still expected a `str` result), which worked by chance in many cases, except for e.g. b'0.0.0.0', which was returned unchanged, breaking later code. Instead of calling `socket.getfqdn()`, we can also use `self.server_name` from the base `HTTPServer` class, which already stores the FQDN of the locally-bound socket name (see `BaseHTTPServer.py` in the Python 2 stdlib and `http/server.py` in the Python 3 stdlib).