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This avoids an ordering dependency between this and the vi-mode plugin.

Uses `is-at-least` instead of a numeric comparison hack, so versions with non-numeric bits like "4.5.0-dev5" don't throw errors.

The old implementation would attempt to load both the default and custom
implementations, with the custom one coming first, so it would get clobbered
by the default version.

Updates OMZ's copy to commit 2c295432175990c1bb4e90bc13f609daa67a25d6 from zsh-users/zsh-history-substring-search

Rather than trying to emulate `git commit --amend` using mercurial queues (which might have side effects if you're using MQ for other things) use the `commit --amend` command which was introduced in Mercurial 2.2 (2012-05-01).

- Delete useless #!zsh
- Simplify gradle build file check
- Format comments and delete TODO stuff (already dealt with)
- Use `$()` syntax for cat commands

In bindkey strings, "^[" and "\e" mean the same thing. They're both notations for Escape.

The zle-line-init and zle-line-finish definitions here were broken with
respect to smkx/rmkx because their "if" logic had fallthrough where it shouldn't,
so the mode was left in rmkx all the time. This just removes those widgets
entirely, because they're now defined (correctly) in lib/keybindings.zsh and
not needed in plugins.

Closes #4616
Changes the `plugins=(... mercurial ...)` to be closer to correct zsh syntax, removing commas and extra spaces.
Revises discussion on configuring themes to avoid sounding like users should modify the theme definition file in the main OMZ folder. Prioritizes the suggestion of using a theme which already supports hg_prompt_info.

Two similar aliases which were causing issues.

Removes old completion setup that breaks with current _git and _hub completions.
Ruby is no longer required by hub; removes that test.
Does not define new completions for hub; they are now defined by hub itself.
Change the functions to use hub to create the repos on GitHub.
Add error checking to the functions.
Removes apparently-unused _github completion definition.

Closes #3248
Closes #4570

* `cfp` alias was referencing an old version of the `cf` command which
no longer exists. This has been updated to reference a valid command.

Check pyenv-virtualenv can eval before use it.
Signed-off-by: Superbil <superbil@gmail.com>