[RFC] Allowing new eof whitelines while still doing whitespace trailing-space fix.

As part of a current mirroring project of a dirty upstream repo that has
mixed line endings and leading/trailing whitespace issues it became
apparent that the current trailing-space fixing in ws.c worked
correctly, but the new_blank_lines_at_end processing in builtin-apply.c
would remove the newly fixed line.  Also, as noted in a previous thread,
there are times when adding new whitelines at eof is a needed
capability, yet the desire remains to correct other whitespace issues
within the patch.

The patch in the follow-up post is an attempt to fix that.  This is my
first git-core patch, so please be honest but gentle. :P  If the fix is
of interest I'd be glad to go through the steps of making a test case
and whatever else is needed.