tests: run many tests in $TESTTMP/repo instead of $TESTTMP
This is useful so we can store other files in $TESTTMP
(in particular tests that use docket files (nodemap, dirstate-v2) keep
file uids in $TESTTMP/UID)
$ hg init repo
$ cd repo
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls -A
.hg
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
.hg
a