Figure out what filenames match the completion.

def real_filename_complete(self, text, line, begidx, endidx):
        """Figure out what filenames match the completion."""

        # line contains the full command line that's been entered so far.
        # text contains the portion of the line that readline is trying to complete
        # text should correspond to line[begidx:endidx]
        #
        # The way the completer works text will start after one of the characters
        # in DELIMS. So if the filename entered so far was "embedded\ sp" then
        # text will point to the s in sp.
        #
        # The following bit of logic backs up to find the real beginning of the
        # filename.

        if begidx >= len(line):
            # This happens when you hit TAB on an empty filename
            before_match = begidx
        else:
            for before_match in range(begidx, 0, -1):
                if line[before_match] in DELIMS and before_match >= 1 and line[before_match - 1] != '\\':
                    break

        # We set fixed to be the portion of the filename which is before text
        # and match is the full portion of the filename that's been entered so
        # far (that's the part we use for matching files).
        #
        # When we return a list of completions, the bit that we return should
        # just be the portion that we replace 'text' with.

        fixed = unescape(line[before_match+1:begidx]) # fixed portion of the match
        match = unescape(line[before_match+1:endidx]) # portion to match filenames against

        # We do the following to cover the case that the current directory
        # is / and the path being entered is relative.
        strip = ''
        if len(match) > 0 and match[0] == '/':
            abs_match = match
        elif cur_dir == '/':
            abs_match = cur_dir + match
            strip = cur_dir
        else:
            abs_match = cur_dir + '/' + match
            strip = cur_dir + '/'

        completions = []
        prepend = ''
        if abs_match.rfind('/') == 0:  # match is in the root directory
            # This means that we're looking for matches in the root directory
            # (i.e. abs_match is /foo and the user hit TAB).
            # So we'll supply the matching board names as possible completions.
            # Since they're all treated as directories we leave the trailing slash.
            with DEV_LOCK:
                if match[0] == '/':
                    completions += [dev.name_path for dev in DEVS if dev.name_path.startswith(abs_match)]
                else:
                    completions += [dev.name_path[1:] for dev in DEVS if dev.name_path.startswith(abs_match)]
            if DEFAULT_DEV:
                # Add root directories of the default device (i.e. /flash/ and /sd/)
                if match[0] == '/':
                    completions += [root_dir for root_dir in DEFAULT_DEV.root_dirs if root_dir.startswith(match)]
                else:
                    completions += [root_dir[1:] for root_dir in DEFAULT_DEV.root_dirs if root_dir[1:].startswith(match)]
        else:
            # This means that there are at least 2 slashes in abs_match. If one
            # of them matches a board name then we need to remove the board
            # name from fixed. Since the results from listdir_matches won't
            # contain the board name, we need to prepend each of the completions.
            with DEV_LOCK:
                for dev in DEVS:
                    if abs_match.startswith(dev.name_path):
                        prepend = dev.name_path[:-1]
                        break

        paths = sorted(auto(listdir_matches, abs_match))
        for path in paths:
            path = prepend + path
            if path.startswith(strip):
                path = path[len(strip):]
            completions.append(escape(path.replace(fixed, '', 1)))
        return completions