Cope with parallel BSD make -jN semantics.

Cope with parallel BSD make -jN semantics.

When BSD `make -jN' is used without `-B' which enables backwards
compatible semantics, it may reuse the same shell for several
commands within a rule; so ensure we do not leave it in a
different directory, nor `exit 0' early in a multi-command rule.

* lib/am/distdir.am (distcheck): After running `distcleancheck',
change back to original working directory.
* lib/am/remake-hdr.am (%CONFIG_HIN%): Run autoheader in a
subshell.
* lib/am/mans.am (uninstall-man%SECTION%): Do not `exit 0' early
in a rule that consists of several shell invocations.  Parallel
NetBSD `make -jN' without `-B' will use only one shell for all
commands, but won't respawn one after `exit 0'.  Fixes
notrans.test failure.
* tests/makej2.test: New test.
* tests/Makefile.am: Update.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>