tests/sitecustomize.py

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.

try:
    import coverage
    getattr(coverage, 'process_startup', lambda: None)()
except ImportError:
    pass