fix for backref error (#258)

Author: willmcgugan

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [2.2.2] - Unreleased
+
+### Fixed
+
+- IllegalBackReference had mangled error message
+
 ## [2.2.1] - 2018-01-06
 
 ### Fixed

fs/_version.py

@@ -1,3 +1,3 @@
 """Version, used in module and setup.py.
 """
-__version__ = "2.2.1"
+__version__ = "2.2.2a0"

fs/path.py

@@ -66,7 +66,7 @@ def normpath(path):
         >>> normpath("foo/../../bar")
         Traceback (most recent call last)
             ...
-        IllegalBackReference: Too many backrefs in 'foo/../../bar'
+        IllegalBackReference: path 'foo/../../bar' contains back-references outside of filesystem"
 
     """
     if path in "/":
@@ -86,7 +86,7 @@ def normpath(path):
             else:
                 components.append(component)
     except IndexError:
-        raise IllegalBackReference("Too many backrefs in '{}'".format(path))
+        raise IllegalBackReference(path)
     return prefix + "/".join(components)