Fix crashitem names mismatch between client and server.

[esoma]

Fixes #172.

The identifier used for the failures/reruns DB is inconsistent, on the client side it is built as:

pytest-rerunfailures/pytest_rerunfailures.py

Lines 485 to 488 in 02c2df7

	item_location = (item.location[0] + "::" + item.location[2]).replace("\\", "/")
	db = item.session.config.failures_db
	item.execution_count = db.get_test_failures(item_location)
	db.set_test_reruns(item_location, reruns)

But on the server:

pytest-rerunfailures/pytest_rerunfailures.py

Lines 339 to 340 in 02c2df7

	reruns = db.get_test_reruns(crashitem)
	if db.get_test_failures(crashitem) < reruns:

This can lead to inconsistent behavior with crash restarts. Sometimes the client side will create an identifier that consists of a full/absolute path while the server's identifier only contains the relative part. As a result, the server gets reruns as 0 and doesn't do a rerun.

[icemac]

LGTM.