tests/test-debugrename.t

store: replace invocation of "getsize()" by "vfs.stat()"

This patch replaces invocation of "getsize()", which calls "os.stat()"
internally, by "vfs.stat()".

The object referred by "self.rawvfs" is used internally by
"_fncachevfs" and doesn't encode filename for each file API invocation.

This patch invokes "os.stat()" via "self.rawvfs" to avoid redundant
filename encoding: invocation of "os.stat()" via "self.vfs" hides
filename encoding and encoding result from caller, so it is not
appropriate, when both encoded and non-encoded filenames should be
yield.

Even though changeset b42b0729744d improved stream_out performance by
"self.pathsep + path", this patch replaces it by
"os.path.join(self.base, path)" of vfs. So, this may increase cost to
join path components.

But this shouldn't have large impact, because:

  - such cost is much less than cost of "os.stat()" which causes
    system call invocation

  - "datafiles()" of store object is invoked only for "hg manifest
    --all" or "hg verify" which are both heavy functions

  $ 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