running `bzr diff` in a subdirectory does not show changes in the parent directory

[Dato Simó]

With bzr.dev (r3144), I just noticed that running `bzr diff` in a
subdirectory does not show changes to files in the root of the branch.
This was confirmed on irc by Martin Albisetti as well.

 affects /products/bzr

[Matthew Fuller (fullermd)]

This came in with rev 3119 ("diff on branches without working trees (Ian Clatworthy, #6700)").

The following is me wildly guessing, and should be taken with several 5-pound value bags of salt. Glancing at the code, this (in bzrlib/diff.py) does look suspicious:

+ if path_list is None or len(path_list) == 0:
+ # If no path is given, assume the current directory
+ default_location = u'.'

BzrDir.open_containing_tree_or_branch() then passes back the relpath from there, which is stuffed into specific_files, which is then passed into show_diff_trees(). Presumably, then, s_d_t() things it's being given the same thing as "bzr diff .".