tests/test-debugrename.t

run-tests: also follow symlink when update PATH with 'run-tests.py' dir

I'm using 'run-tests.py' from my '$PATH' and use a symlink to get 'run-tests.py'
to in that '$PATH'. There is a handful of test helpers (like f) that needs to be
in the '$PATH' for the test to run, and they are expected to live next to the
'run-tests.py' binary. Using a symlink confuses this logic, so we add to the
'$PATH' both the 'run-tests.py' executable directory, and the actual file
location direction.

  $ hg init
  $ echo a > a
  $ hg ci -Am t
  adding a

  $ hg mv a b
  $ hg ci -Am t1
  $ hg debugrename b
  b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3

  $ hg mv b a
  $ hg ci -Am t2
  $ hg debugrename a
  a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980

  $ hg debugrename --rev 1 b
  b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3