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-pycparser/package.py

@@ -28,8 +28,11 @@
 class PyPycparser(PythonPackage):
     """A complete parser of the C language, written in pure python."""
     homepage = "https://github.com/eliben/pycparser"
-    url      = "https://pypi.python.org/packages/source/p/pycparser/pycparser-2.13.tar.gz"
+    url      = "https://pypi.io/packages/source/p/pycparser/pycparser-2.17.tar.gz"
 
+    import_modules = ['pycparser', 'pycparser.ply']
+
+    version('2.17', 'ca98dcb50bc1276f230118f6af5a40c7')
     version('2.13', 'e4fe1a2d341b22e25da0d22f034ef32f')
 
     depends_on('py-setuptools', type='build')