tests/test-symlinks.out

hgmerge: add cleanup functions

This patch adds functions cleanup, success and failure.
The last two of these should be used instead of exit.
Current code was changed to use them.
It also moves $HGTMP to the top of the file (it's used in the cleanup
function), changes the comment and removes now unneeded trap
in the diff+patch merge.

adding foo
adding bomb
adding a.c
adding dir/a.o
adding dir/b.o
! a.c
! dir/a.o
! dir/b.o
? .hgignore
a.c: unsupported file type (type is fifo)
! a.c