bdiff-torture: fix pyflakes warning reporting undefined name 'inst'

Looks like I got a latest version of pyflakes somehow or it's running on py3 and
it spotted this.

Differential Revision: https://phab.mercurial-scm.org/D6757

contrib/bdiff-torture.py

@@ -1,99 +1,98 b''
 # Randomized torture test generation for bdiff
 
 from __future__ import absolute_import, print_function
 import random
 import sys
 
 from mercurial import (
     mdiff,
 )
 
 def reducetest(a, b):
     tries = 0
     reductions = 0
     print("reducing...")
     while tries < 1000:
         a2 = "\n".join(l for l in a.splitlines()
                        if random.randint(0, 100) > 0) + "\n"
         b2 = "\n".join(l for l in b.splitlines()
                        if random.randint(0, 100) > 0) + "\n"
         if a2 == a and b2 == b:
             continue
         if a2 == b2:
             continue
         tries += 1
 
         try:
             test1(a, b)
         except Exception:
             reductions += 1
             tries = 0
             a = a2
             b = b2
 
     print("reduced:", reductions, len(a) + len(b),
           repr(a), repr(b))
     try:
         test1(a, b)
     except Exception as inst:
         print("failed:", inst)
 
     sys.exit(0)
 
 def test1(a, b):
     d = mdiff.textdiff(a, b)
     if not d:
         raise ValueError("empty")
     c = mdiff.patches(a, [d])
     if c != b:
         raise ValueError("bad")
 
 def testwrap(a, b):
     try:
         test1(a, b)
         return
     except Exception as inst:
-        pass
     print("exception:", inst)
     reducetest(a, b)
 
 def test(a, b):
     testwrap(a, b)
     testwrap(b, a)
 
 def rndtest(size, noise):
     a = []
     src = "                aaaaaaaabbbbccd"
     for x in xrange(size):
         a.append(src[random.randint(0, len(src) - 1)])
 
     while True:
         b = [c for c in a if random.randint(0, 99) > noise]
         b2 = []
         for c in b:
             b2.append(c)
             while random.randint(0, 99) < noise:
                 b2.append(src[random.randint(0, len(src) - 1)])
         if b2 != a:
             break
 
     a = "\n".join(a) + "\n"
     b = "\n".join(b2) + "\n"
 
     test(a, b)
 
 maxvol = 10000
 startsize = 2
 while True:
     size = startsize
     count = 0
     while size < maxvol:
         print(size)
         volume = 0
         while volume < maxvol:
             rndtest(size, 2)
             volume += size
             count += 2
         size *= 2
     maxvol *= 4
     startsize *= 4