test: explicitly "add" file before some commit in test-filecache.py
`hg commit -A` will revert the `hg addremove` step if the commit fails. However
`hg rollback` currently does not.
We are about to improve internal consistency around transaction and dirstate and the behavior of `hg rollback` will align on the other behavior in the process.
Before doing so, we make sure the test is using a separate call to `hg add` to
avoid the test scenario to be affected by that future change.
note: the behavior change for `hg rollback` seems fine as it affect a niche
usecase and `hg rollback` usage have been strongly discouraged for a while.
#if no-windows no-osx
$ mkdir -p xdgconf/hg
$ echo '[ui]' > xdgconf/hg/hgrc
$ echo 'username = foobar' >> xdgconf/hg/hgrc
$ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
$ unset HGRCPATH
$ hg config ui.username 2>/dev/null
foobar
#endif