Added rules to Makefile.buildbot for generating coverage reports

.coveragerc

@@ -0,0 +1,3 @@
+[run]
+include = scrapy/*
+omit = scrapy/xlib*,scrapy/tests*

Makefile.buildbot

@@ -1,6 +1,21 @@
+TRIAL := $(shell which trial)
+COVERAGE_DIR ?= "htmlcov"
+
 deb:
 	python extras/makedeb.py build
 
 deb-clean:
 	debclean
 	python extras/makedeb.py clean
+
+# Generate coverage reports
+# Requires: coverage 3.3 or above from http://pypi.python.org/pypi/coverage
+coverage-report:
+	coverage run --branch ${TRIAL} --reporter=text scrapy.tests
+	coverage html -i -d "${COVERAGE_DIR}"
+
+coverage-view: coverage-report
+	python -m webbrowser "${COVERAGE_DIR}"
+
+coverage-clean:
+	rm -rf .coverage "${COVERAGE_DIR}"