It appears that when the subshell has a ||, the 'set -e' within
subshell gets invalidated.

This will work as expected:

 ( set -e; false; echo "should not get here" )

While this will not work as expected:

 ( set -e; false; echo "should not get here" ) || false

We resolve it by using $? to detect the status of subshell. We also let
the exitcode indicate how many packages that failed.

While here we also refactor it so most of the loop happens within the
subshell. This lets us set (or increase) rc variable once, and it
reduces number of forks which gives slightly better performance.

We actually want be able to re-run abump without needing reset the
pkgver in case we had to fix things.

This reverts commit 8198ded868d4b7b98f8d06a2f0f0d90eaf2ad9da.

Conflicts:
	abump.in

Otherwise abuild-sign will end with error

This permits introducing branch-specific modifications to abuild.conf settings.
Any settings there override /etc/abuild.conf and $HOME/.abuild/abuild.conf.