On Ubuntu systems, /bin/sh is actually "dash". "pushd" and "popd"
don't work with "dash". So we now use "cd" instead, thus lowering
requirements for shell.
This defect was causing "unknown" svn version in logs when jack was
build using dash.
git-svn-id: http://subversion.jackaudio.org/jack/jack2/trunk/jackmp@3085 0c269be4-1314-0410-8aa9-9f06e86f4224