map: Support remotes with /~/ and /~user/

More accurately, it was supported already when map uses git-annex-shell,
but not when it does not.

Note that the user name cannot be shell escaped using git-annex's current
approach for shell escaping. I tried and some shells like dash cannot
cd ~'joey'. Rest of directory is still shell escaped, not for security but
in case a directory has a space or other weird character.

doc/bugs/git_annex_map_has_problems_with_urls_containing___126__.mdwn

@@ -42,3 +42,5 @@ map` works too:
 
     ok
 
+
+> [[fixed|done]] --[[Joey]]