profiling: replace '+' markup of nested lines with indentation
The display of nested lines for hg --profile was very non-obvious and made it
look like sort didn't work.
The '+' immediately before CallCount was not related to the CallCount and did
not mean plus in any integer sense.
The '+' before module looked like a part of the module name and not like ascii
art.
Instead we now indent the subordinate module names to clearly show the
structure.