parsers: clarify documentation of test-parseindex2.py

This change updates and improves the description of test-parseindex2.py.
In particular, it removes language that can be interpreted to mean that the
test module checks only the C implementation of parsers.parse_index2().
Rather, the module checks parsers.parse_index2(), which can be either the
C or pure Python implementation, depending on which version is being used.

As of e57c532c3835, the module also does more than just compare the return
value with the original Python implementation.

tests/test-parseindex2.py

@@ -1,11 +1,9 b''
+"""This unit test tests parsers.parse_index2()."""
+
 from mercurial import parsers
 from mercurial.node import nullid, nullrev
 import struct
 
-# This unit test compares the return value of the original Python
-# implementation of parseindex and the new C implementation for
-# an index file with and without inlined data
-
 # original python implementation
 def gettype(q):
     return int(q & 0xFFFF)
@@ -106,6 +104,9 b' def runtest() :'
     else:
         print "Expected to get TypeError."
 
+   # Check parsers.parse_index2() on an index file against the original
+   # Python implementation of parseindex, both with and without inlined data.
+
     py_res_1 = py_parseindex(data_inlined, True)
     c_res_1 = parse_index2(data_inlined, True)