Dynamically complete the filename at point.
Completes if after a filename.
This function is similar to `comint-replace-by-expanded-filename', except that
it won't change parts of the filename already entered in the buffer; it just
adds completion characters to the end of the filename. A completions listing
may be shown in a separate buffer if completion is ambiguous.
Completion is dependent on the value of `comint-completion-addsuffix',
`comint-completion-recexact' and `comint-completion-fignore', and the timing of
completions listing is dependent on the value of `comint-completion-autolist'. Returns t if successful. (fn)