dockerdeb: redirect 'cd' in export command to /dev/null
This had the unfortunate side effect of causing the environment to have a
newline due to the fact that some 'cd' outputs the result of the directory
change. So, let's just redirect the meaningless output.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a