more shell-pcomplete UI regressions

[Noah Friedman]

I cannot complete file names that have spaces in them, even if I put
backslashes in front of the spaces.

For instance this used to work:

    ~ $ ls /com/mp3/albums/King\ Cr<TAB>
    -| ~ $ ls /com/mp3/albums/King\ Crimson/

But now I get no matches even though "King Crimson" shows up in the
completions window if I type King<TAB>.  (If I pick some name that doesn't
have many possible completions then one of them is inserted into the
buffer; but if there are many, there is currently no way for me to finish
the match manually so that the rest will complete.)

Also, this fails:

    ~ $ ls '/com/mp3/albums/King<TAB>
    ->  (file-error "Opening directory" "no such file or directory" 
"/home/friedman/'/com/mp3/albums/")

In the old comint-dynamic-complete world, the leading quote enables
comint-dynamic-complete to insert filenames without backslashifying all the
spaces or other shell metacharacters.