Fix bash completion when using command options

By quoting the ‘line’ variable we are making it a single word, but ‘getopts’ wants each option as its own word.

Previously bash completion would output an error for a line like: ‘ninja -vn targ‸’.

In addition to removing the quotes (to enable word expansion) I also used it as a regular variable, as that is what it is (not an array).
Expand the -C argument via ‘eval’ in bash completion

Previously completion would not work for ‘ninja -C $HOME/Source/foo targ‸’.

We still do not support using tilde in the directory argument.
Merge pull request #737 from sorbits/bash-completion-fixes

Bash completion fixes