cleanpatch: a script to clean up stealth whitespace added by a patch

This script is a companion to the "cleanfile" script.  This cleans
up a patch in unified diff format *before* it is applied.  Note that
the empty lines at the end of file detection *requires* that the diff was
taken with at least one line of context around each hunk, or bad things
will happen.

This script cleans up various classes of stealth whitespace.  In
particular, it cleans up:

- Whitespace (spaces or tabs)before newline;
- DOS line endings (CR before LF);
- Space before tab (spaces are deleted or converted to tabs);
- Empty lines at end of file.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>