Use prefixes, import functionality.

hungry-delete-forward and -backward are extensions of
delete-forward-char and delete-backward-char. Recent patches took into
account that those original versions work in Delete Selection mode /
Transient Mark mode. This patch takes into account that the originals
use prefix arguments.

Not only does this allow deleting a specific number of
characters (whitespace or otherwise), but it also means that Hungry can
basically mimic all of the stock features of the original versions,
including untabifying with Overwrite mode.
More accurate check for prefix argument.

Someone might want to explicitly give a prefix of one. In the previous
implementation, such an event would call the relevant hungry-*-iter,
which *might indeed* delete one forward or backward character, but only
if that character was not whitespace. If it was whitespace, it would get
HUNGRY!

This implementation tests whether or not a prefix has explicitly been
given, not whether or not the prefix is equal to one. Thus, someone can
explicitly use these functions to delete one whitespace character, as
well as any number of anything characters.
Merge pull request #10 from mwfogleman/prefix

Use prefixes, import functionality.