backslash escape dash, fix #167

[paralax]

with the backslash:

In [15]: Q = re.compile(r'[^a-zA-Z0-9_.\-=]', re.DEBUG)
in
  negate None
  range (97, 122)
  range (65, 90)
  range (48, 57)
  literal 95
  literal 46
  literal 45
  literal 61

without it:

In [10]: Q = re.compile(r'[^a-zA-Z0-9_.-=]', re.DEBUG)
in
  negate None
  range (97, 122)
  range (65, 90)
  range (48, 57)
  literal 95
  range (46, 61)