bash-completion erases "if=" when using autocomplete with the dd command.

[Mateo Salta]

Both my 14.04 and 15.10 install. using dd in a folder with the syntax `sudo dd if=[type letters and hit tab]` will start to auto-complete but erase `if=` and fail to continue to autocomplete.

Steps -
1. Type out a dd command `sudo dd if=`
2. Type beginning letters of an existing file.
3. Hit tab to initiate auto-complete.

What should happen
- autocomplete will put in the file name after if= and allow continuation and suggestions of the rest of the filename.

What happens
- the file name erases if= and prevents further autocomplete action

------
`lsb_release -rd
Description: Ubuntu 15.10
Release: 15.10

apt-cache policy bash-completion
bash-completion:
  Installed: 1:2.1-4.1ubuntu2
  Candidate: 1:2.1-4.1ubuntu2
  Version table:
 *** 1:2.1-4.1ubuntu2 0
        500 http://us.archive.ubuntu.com/ubuntu/ wily/main amd64 Packages
        100 /var/lib/dpkg/status`

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Aapo Rantalainen (aapo-rantalainen)]

Couple of notes:
This bug happens also without sudo.
This bug happens also for of= and conv=

[Aapo Rantalainen (aapo-rantalainen)]

This is fixed in Ubuntu-16.04
with bash-completion: 1:2.1-4.2ubuntu1