Rework Spack's Mercurial support (#3834)

* Add tests to mercurial package

* Add support for --insecure with mercurial fetching

* Install man pages and tab-completion scripts

* Add tests and latest version for all deps

* Flake8 fix

* Use certifi module to find CA certificate

* Flake8 fix

* Unset PYTHONPATH when running hg

* svn_fetch should use to svn-test, not hg-test

* Drop Python 3 support in Mercurial

Python 3 support is a work in progress and isn't currently
recommended:

https://www.mercurial-scm.org/wiki/SupportedPythonVersions

* Test both secure and insecure hg fetching

* Test both secure and insecure git and svn fetching

var/spack/repos/builtin/packages/py-pygments/package.py

@@ -29,8 +29,14 @@ class PyPygments(PythonPackage):
     """Pygments is a syntax highlighting package written in Python."""
 
     homepage = "https://pypi.python.org/pypi/pygments"
-    url      = "https://pypi.python.org/packages/source/P/Pygments/Pygments-2.0.1.tar.gz"
+    url      = "https://pypi.io/packages/source/P/Pygments/Pygments-2.2.0.tar.gz"
 
+    import_modules = [
+        'pygments', 'pygments.filters', 'pygments.formatters',
+        'pygments.lexers', 'pygments.styles'
+    ]
+
+    version('2.2.0', '13037baca42f16917cbd5ad2fab50844')
     version('2.1.3', 'ed3fba2467c8afcda4d317e4ef2c6150')
     version('2.0.1', 'e0daf4c14a4fe5b630da765904de4d6c')
     version('2.0.2', '238587a1370d62405edabd0794b3ec4a')