tests/test-merge-subrepos.t

subrepo: make "_sanitize()" take absolute path to the root of subrepo

Before this patch, "hg update" doesn't sanitize ".hg/hgrc" in non-hg
subrepos correctly, if "hg update" is executed not at the root of the
parent repository.

"_sanitize()" takes relative path to subrepo from the root of the
parent repository, and passes it to "os.walk()". In this case,
"os.walk()" expects CWD to be equal to the root of the parent
repository.

So, "os.walk()" can't find specified path (or may scan unexpected
path), if CWD isn't equal to the root of the parent repository.

Non-hg subrepo under nested hg-subrepos may cause same problem, too:
CWD may be equal to the root of the outer most repository, or so.

This patch makes "_sanitize()" take absolute path to the root of
subrepo to sanitize correctly in such cases.

This patch doesn't normalize the path to hostile files as the one
relative to CWD (or the root of the outer most repository), to fix the
problem in the simple way suitable for "stable".

Normalizing should be done in the future: maybe as a part of the
migration to vfs.

  $ hg init

  $ echo a > a
  $ hg ci -qAm 'add a'

  $ hg init subrepo
  $ echo 'subrepo = http://example.net/libfoo' > .hgsub
  $ hg ci -qAm 'added subrepo'

  $ hg up -qC 0
  $ echo ax > a
  $ hg ci -m 'changed a'
  created new head

  $ hg up -qC 1
  $ cd subrepo
  $ echo b > b
  $ hg add b
  $ cd ..

Should fail, since there are added files to subrepo:

  $ hg merge
  abort: uncommitted changes in subrepository 'subrepo'
  [255]