transitive copy/rename
Add support for transitive copy or rename operations, e.g.
hg rename a b
... (possibly edit b)
hg rename b c
hg commit ...
by actually renaming "b" as "c" while recording a copy of
"a" to "c" and a removal of "a".
%% no merges expected
%% merge should fail
abort: 'b' already exists in the working dir and differs from remote
%% merge of b expected
merging for b
merging b
%%
Contents of b should be "this is file b1"
This is file b1
%% merge fails
abort: outstanding uncommited changes
%% merge expected!
merging for b
merging b
%% merge of b should fail
abort: outstanding uncommited changes
%% merge of b expected
merging for b
merging b