fixed fish-shell/fish-shell#944

When the completion list includes the exact typed string with other
candidates, i.e. completion_t.match.type == fuzzy_match_exact,
the other candidates will be removed from the list, as they are not
the "best type". This is inconvenient for the user who wants to
type and complete commands in the other candidates.

The commit is to make the best_type to fuzzy_match_prefix as highest
priority, also, when comparing to best_type, the same or higher
priority completions can both match.
improve comments and extract a common function
Clean up some comments and make a function static
Fix #976. Now prompt tries to use standard git command.
Fix bad error message for certain options.
https://github.com/fish-shell/fish-shell/issues/979
Stop insisting on trying to add /usr/bin and /bin to $PATH.
https://github.com/fish-shell/fish-shell/pull/854
Add a fancy new paths_are_equivalent function to test for equivalent
paths instead of merely equal ones
libncursesw5-dev is not needed on Debian

I just checked on new Debian installation, and only libncurses5-dev appears to be needed.
Initialize cycle_cursor_pos.

This removes the warning from compiler.
Put an IRC link to README.
Replace IRC link with WebChat link

It seems GitHub doesn't allow irc:// protocol, so replace it with WebChat link.
Support iTerm2 forward/backward word escapes
(https://github.com/fish-shell/fish-shell/issues/920)
Adjust prefix completions to sort alphabetically instead of by length.
Other completions are still sorted by length.
https://github.com/fish-shell/fish-shell/issues/923
Try to improve the error message printed when libcurses is not found
Fix indentation
Fix more indentation in fish_default_key_bindings.fish
completion for vim-addons
docs: don't remove/rebuild share/man if we don't have doxygen
Fix useradd completion syntax
(https://github.com/fish-shell/fish-shell/issues/863)
git version generation fixes

- Remove the `version` file created for the tarball after the tarball is finished
- Use the builtin type instead of which.