require: provide a link to a wiki page in addition of suggesting upgrade

The wiki page is intended to describe several solution to the requirement issue.
Some of those solutions does not involve upgrading mercurial. That is very
useful for people that can't easily upgrade they Mercurial in some place.
revset: add 'only' revset

Adds a only() revset that has two forms:

only(<set>) is equivalent to "::<set> - ::(heads() - heads(<set>::))"

only(<include>,<exclude>) is equivalent to "::<include> - ::<exclude>"

On a large repo, this implementation can process/traverse 50,000 revs in 0.7
seconds, versus 4.2 seconds using "::<include> - ::<exclude>".

This is useful for performing histedits on your branch:
hg histedit -r 'first(only(.))'

Or lifting branch foo off of branch bar:
hg rebase -d @ -s 'only(foo, bar)'

Or a variety of other uses.
setup: specify --prefix="" for install-home-bin to avoid badness with defaults

Sometimes (I'm not sure when) setup.py gets a default value for
--prefix, which breaks --home. This fixes that for me.
revset: added orderedlazyset class
revset: added _intlist method to replace _list for %ld

Now %ld expression goes through _intlist and doesn't do any unnecesary
processing anymore.
localrepo: language and spelling fixes in comment
merge with stable
revset: added _hexlist method to replace _list for %ln

Now %ln expression goes through _hexlist and doesn't do any unnecesary
processing anymore.
config: move showconfig code and add config as primary alias

Preparation for adding config --edit to launch an editor
revert: extract actual revert in its own function

With this small refactoring, the computation of the action to perform and the
actual change to the disk happen in different function. This allows extension to
wrap the later in case of need. The initial motivation is the `remotefilelog`
extension that need to prefetch all the file content to be checked out.
config: add initial implementation of --edit

This launches the preferred editor on either:

a) the first non-empty user rc file found
b) the first user rc file in the search list
config: add example config file when -e called with no config
test-help.t: add test for 'hg help extensions'

This demonstrates the defect that deprecated extensions show up in the
output. A followup patch will fix this defect.
help: exclude deprecated extensions in the disabled part of 'help extensions'
ui: suggest config --edit when no username is set
merge with stable
tests: fix up config --edit breakage
ui: fix extra space in username abort
merge with crew
obsstore: `create` method return True if a marker is actually added

The obsstore method now have a return value. This informs caller about the
actual creation of a new markers. No new markers are created if it would have
been a duplicate.