Handle default install --options
Handle default install --options

i.e. `--force --debug --use-llvm --ignore-dependencies --HEAD`

Additionally:

 * Use a cleaner `if` block in install options completion case.
 * De-dupe options for subsequent completion (e.g. stop offering --foo once
   --foo option has been used).

Signed-off-by: Adam Vandenberg <34c2b6407fd5a10249a15d699d40f9ed1782e98c@gmail.com>

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