tests/test-diffdir

hgmerge: fix diff+patch detection; cleanups

Details:
  - actually show help message when no tools are found
  - whitespace cleanup (stupid emacs)
  - quote more variables
  - simplify merge/diff3 error handling

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "0 0"

echo 123 > b
hg add b
hg diff | sed -e "s/\(+++ [a-zA-Z0-9_/.-]*\).*/\1/" \
              -e "s/\(--- [a-zA-Z0-9_/.-]*\).*/\1/"

hg diff -r tip | sed -e "s/\(+++ [a-zA-Z0-9_/.-]*\).*/\1/" \
                     -e "s/\(--- [a-zA-Z0-9_/.-]*\).*/\1/"

echo foo > a
hg diff | sed -e "s/\(+++ [a-zA-Z0-9_/.-]*\).*/\1/" \
              -e "s/\(--- [a-zA-Z0-9_/.-]*\).*/\1/"