resolves issue #59

resolves issue #48

Have the path.pyimport() helper raise an EnvironmentError if an
import of a given file returns a module that does not appear to
be coming from the actual path.  E.g. for a directory layout like this:

    a / test_whatever.py
    b / test_whatever.py

calling py.path.local("b/test_whatever.py").pyimport() will
fail if the other globally scoped test_whatever module was
loaded already.

--HG--
branch : trunk

_py/path/local.py

@@ -516,7 +516,16 @@ class LocalPath(FSBase):
                     self._prependsyspath(self.dirpath())
                 modname = self.purebasename
             mod = __import__(modname, None, None, ['__doc__'])
-            #self._module = mod
+            modfile = mod.__file__
+            if modfile[-4:] in ('.pyc', '.pyo'):
+                modfile = modfile[:-1]
+            elif modfile.endswith('$py.class'):
+                modfile = modfile[:-9] + '.py'
+            if not self.samefile(modfile):
+                raise EnvironmentError("mismatch:\n"
+                "imported module %r\n"
+                "does not stem from %r\n" 
+                "maybe __init__.py files are missing?" % (mod, str(self)))
             return mod
         else:
             try:

_py/test/plugin/pytest_pytester.py

@@ -70,6 +70,12 @@ class TmpTestdir:
             py.std.sys.path.remove(p)
         if hasattr(self, '_olddir'):
             self._olddir.chdir()
+        # delete modules that have been loaded from tmpdir
+        for name, mod in list(sys.modules.items()):
+            if mod:
+                fn = getattr(mod, '__file__', None)
+                if fn and fn.startswith(str(self.tmpdir)):
+                    del sys.modules[name]
 
     def getreportrecorder(self, obj):
         if isinstance(obj, py._com.Registry):