Fix errors in eshell prompt function
Fix errors in eshell prompt function

To determine whether a merge is in progress, do not check in the current
directory for .git/MERGE_HEAD, but do this in the repository directory.

When computing `base-dir`, take the whole non-directory part, not just the
basename; otherwise directories like .emacs.d will get the final `.d` get
stripped off.

exot/.emacs.d