Patch version from Hans Meine from the duistutils mail list.
https://mail.python.org/pipermail/distutils-sig/2008-April/009336.html
http://mail.python.org/pipermail/distutils-sig/attachments/20080414/16fb135e/attachment-0001.diff

Add copy_inc_files function to fix issue of lost pyconfig.h.

When sys.exec_prefix and sys.prefix differ the pyconfig.h file
is in $(exec_prefix)/include/python$(version) and that file is
missing in the virtualenv because env/include/python$(version)
is a symlink to $(real_prefix)/include/python$(version).
If --always-copy is used then the two include directories merge.
I added copy_inc_files to symlink (or copy) the individual contents
of prefix include and exec_prefix include into env/include.
Fix expected output to match actual output for setuptools
and pip installation progress.  The progress line has been
one line for a while but the expected output was looking for
two lines.
Fix default args for py.test to be "tests" instead of using the
command name "test" also as the directory name to find tests.
Merge pull request #635 from shidesthewise/feature/testfix-1

Fixes for validating activation output and setuptools test integration.
Fix case where sys.exec_prefix is not a subdir of sys.prefix.
Skip copying required file if exec_prefix != prefix and
the file is sourced from exec_prefix.  Let the
copying/linking of exec_dir in install_python handle
these files.
Merge branch 'feature/testfix-1' into develop
Merge branch 'feature/testfix-2' into develop
Merge branch 'develop' of github.com:pypa/virtualenv into develop