debugcommands: move 'debugpushkey' in the new module

ui: remove urllib2 from being imported early Before this change, urllib2 was brought in when constructing the ui object, and that added ~5ms on my Linux workstation to the hg startup time for every command, bringing the time for 'HGRCPATH=/dev/null hg root' from 46ms to 40ms. Now, we construct a single proxy object per initial ui creation (so that if the ui is copied they share the object), but defer the actual instantiation of it and the import of urllib2 until it's needed. # no-check-commit

tests: switch "this command isn't paged" example to id I'm about to enable pager support in summary.

tests: update test-i18n.t to not depend on the pager extension I'm about to mark that extension as deprecated, and that broke this test.

pager: add a test of --pager=no functionality I'm about to upend the pager universe, but I would like to not regress anything.

hg: allow usage of XDG_CONFIG_HOME/hg/hgrc Modern applications must use the following paths to store configuration files: - $XDG_CONFIG_HOME/hg/hgrc, - $HOME/.config/hg/hgrc (if XDG_CONFIG_HOME is unset or not absolute). For backward compatibility, ~/.hgrc is still created if no hgrc exist using hg config --edit. See https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

debugcommands: move 'debugpathcomplete' in the new module

debugcommands: move 'debugobsolete' in the new module