Set SVN_EDITOR=false, trigger an add-on-add or edit-on-edit property conflict,
and choose 'e' (edit):
[[[
Select: (p) postpone, (mf) my version, (tf) their version,
(dc) display conflict, (e) edit property, (q) quit resolution,
(h) help: e
system('false svn-lLbmsc') returned 1
Select: (p) postpone, (mf) my version, (tf) their version,
(dc) display conflict, (e) edit property, (q) quit resolution,
(h) help:
]]]
Two problems:
1. The error lacks an "svn: " prefix.
2. The error is too low-level; "Running the editor failed:" would not be amiss.
Also, the code that handles SVN_ERR_EXTERNAL_PROGRAM is repeated about half a
dozen times with little changes; consider consolidating those repetitions.