Revision 1.94 of diff-mode.el (committed 2007-01-11) introduced a
regression.  Now, the diff-goto-source function fails with either of
the error messages below if "-p" is present in diff-switches:

    Unrecognized context diff first hunk header format
    Unrecognized unified diff hunk header format

The enclosed patch makes diff-sanity-check-hunk less picky on the
format, so that diff-goto-sources starts working again even if
diff-switches is set to "-p" or "-up".

One way to reproduce the problem is to check out the Emacs source code
from CVS, edit emacs/src/abbrev.c, inserting a character in the
syms_of_abbrev function, saving the buffer, do M-x set-variable RET
diff-switches RET "-up" RET, do M-x vc-diff, move the cursor down to
the character you inserted, and press C-c C-c.  Instead of jumping to
the same place in the source buffer, you will get the second error
message reported above.

    /ceder