Specifier equivalence check does not consider version equivalence

[uranusjr]

Orginally reported as pypa/pip#7900.

Currently the specifier equivalence check compares the contained version as a string. packaging.version.parse should be used instead to ensure equivalent version strings are considered equal.

Minimal reproduction:

>>> from packaging.specifiers import SpecifierSet
>>> SpecifierSet("==2.8.0") == SpecifierSet("==2.8.0")
True
>>> SpecifierSet("==2.8.0") == SpecifierSet("==2.8")
False

[di]

The issue is that the specifiers are not considered equal:

packaging/packaging/specifiers.py

Lines 139 to 149 in d3f305d

	def __eq__(self, other):
	# type: (object) -> bool
	if isinstance(other, string_types):
	try:
	other = self.__class__(str(other))
	except InvalidSpecifier:
	return NotImplemented
	elif not isinstance(other, self.__class__):
	return NotImplemented
	return self._spec == other._spec

>>> from packaging.specifiers import Specifier
>>> Specifier('==2.8.0') == Specifier('==2.8')
False
>>> Specifier('==2.8.0') == Specifier('==2.8.0')
True
>>> Specifier('==2.8.0')._spec
('==', '2.8.0')
>>> Specifier('==2.8')._spec
('==', '2.8')

We should canonicalize the version when comparing them, I created #283 to fix this.