Fix accidental module aliasing

When there was no top-level module or package available in sys.path
(like pylab), but there was a different module/package that was a prefix
of the first module (like py), findimports would incorrectly decide that
they were one and the same!

Fixes #10.

findimports.py

@@ -518,7 +518,7 @@ class ModuleGraph(object):
             candidate = self.isPackage(name, extrapath)
             if candidate:
                 return candidate
-            name = name[:name.rfind('.')]
+            name = name.rpartition('.')[0]
         self.warn(dotted_name, '%s: could not find %s', filename, dotted_name)
         return dotted_name
 

tests/unknown-modules.txt

@@ -19,7 +19,12 @@ We print warnings when we cannot find a module/package
     ... import imaginary.package
     ... ''')
 
+    >>> with open('foo.py', 'w') as f: _ = f.write('''
+    ... # decoy, see https://github.com/mgedmin/findimports/issues/10
+    ... ''')
+
     >>> graph = ModuleGraph()
+    >>> graph.path.append('.')
     >>> graph.parseFile('marmalade.py')
     marmalade.py: could not find foobar
     marmalade.py: could not find imaginary.package