return the error message produced by importlib, so that if an import
in the package whose import is being wrapped is what failed the skip
message will contain the name of that module instead of the name of the
wrapped module.  Also fixed formatting of some previous comments.

tuples, dicts and sets on failure.

Many new handy type and comparison specific assert* methods have been added
that fail with error messages actually useful for debugging.  Contributed in
by Google and completed with help from mfoord and GvR at PyCon 2009 sprints.

Discussion lives in http://bugs.python.org/issue2578.

#1386675: specify WindowsError as the exception, because it has a winerror attribute that EnvironmentError doesnt have.

Re http://bugs.python.org/issue4315

The symbol table used the same name dictionaries to recursively
analyze each of its child blocks, even though the dictionaries are
modified during analysis.  The fix is to create new temporary
dictionaries via the analyze_child_block().  The only information that
needs to propagate back up is the names of the free variables.

Add more comments and break out a helper function.  This code doesn't
get any easier to understand when you only look at it once a year.

to ensure that the build will succeed in a clean
checkout and with a non-default deployment target.

explicit global variables.

inside the catch_warnings context manager.

sys.path on OSX, to make it easier to share (some) installed
packages between the system install and a user install.

should cause tests to be skipped.  Also rename import_function
to the more descriptive get_attribute and add a docstring.

though with some changes by me.  This patch should not be back ported or
forward ported.  It's a bit too risky for 2.6 and 3.x does things fairly
differently.