tests/sitecustomize.py

dirstate: factor common update code into _addpath

Factor update code common to all callers of _addpath into _addpath.
By centralizing the update code here, it provides one place to put
updates to new data structures - in a future patch.  It also removes
a few lines of duplicate code.

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