tests/sitecustomize.py

patch: stop modifying gitpatch objects

gitpatch objects emitted by iterhunks() were referencing file paths unmodified
from the input patch. _applydif() made them usable by modifying the gitpatch
objects in-place with specified path strip level. The same modified objects
were then reused by iterhunks() generator. _applydiff() now copies and update
the paths which completely decouples both routines.

As a side effect, the "git" event now receives only metadata about
copies/renames to perform the necessary copies ahead of time. Other actions are
handled in the "file" event.

try:
    import coverage
    if hasattr(coverage, 'process_startup'):
        coverage.process_startup()
except ImportError:
    pass