Tweak coverage reporting

Author: PiDelport

.coveragerc

@@ -5,3 +5,8 @@ branch = True
 source =
     src
     tests
+
+omit =
+    # This is purely backported test support code:
+    # we don't use all its functionality.
+    tests/script_helper.py

.travis.yml

@@ -9,9 +9,11 @@ matrix:
     - { python: 'pypy', env: TOXENV=pypy }
     - { python: 'pypy3', env: TOXENV=pypy3 }
 
-    # Limit coverage reporting only to the latest Python 2 and 3 versions.
+    # Report coverage for the latest Python 3 and 3 versions, and for PyPy,
+    # to cover all the interesting code paths.
     - { python: '2.7', env: TOXENV=py27-codecov }
     - { python: '3.5', env: TOXENV=py35-codecov }
+    - { python: 'pypy', env: TOXENV=pypy-codecov }
 
   allow_failures:
     # PyPy3 on Travis seems to be broken, as of 2016-02.