Commit 4853a4aad9 used the tmpdir variable
for checking the existence of /bin/sh, without resetting it.
This caused /bin/sh to be deleted during the cleanup part, as soon as a scriptlet
other than pre_upgrade or pre_install was executed.
For example, on the first post_upgrade during a -Su.
I introduced two variables : clean_tmpdir and restore_cwd, for deciding what should
be done in the cleanup part.
Signed-off-by: Chantry Xavier <shiningxc@gmail.com>
3d7e06f204