The test still fails on FreeBSD 7.2, Tiger and Debian parallel:

"""
======================================================================
FAIL: test_siginterrupt_on (test.test_signal.SiginterruptTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/db3l/buildarea/3.x.bolen-freebsd7/build/Lib/test/test_signal.py",
line 379, in test_siginterrupt_on
    self.assertTrue(interrupted)
AssertionError: False is not true

======================================================================
FAIL: test_without_siginterrupt (test.test_signal.SiginterruptTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/home/db3l/buildarea/3.x.bolen-freebsd7/build/Lib/test/test_signal.py",
line 372, in test_without_siginterrupt
    self.assertTrue(interrupted)
AssertionError: False is not true
"""

Here's a sample strace output on my Linux box when it fails:

2120  21:00:18.755448 rt_sigaction(SIGALRM, {0x810b332, [], 0}, NULL,
8) = 0 <0.000019>
2120  21:00:18.755690 alarm(1)          = 0 <0.000024>
2120  21:00:18.755803 read(3,  <unfinished ...>
[...]
2120  21:00:19.755811 <... read resumed> 0xb72cad90, 1) = ?
ERESTARTSYS (To be restarted) <0.999973>
2120  21:00:19.755864 --- SIGALRM (Alarm clock) @ 0 (0) ---
2120  21:00:19.756094 sigreturn()       = ? (mask now []) <0.000019>
2120  21:00:19.756434 alarm(1)          = 0 <0.000023>
2120  21:00:19.756547 read(3,  <unfinished ...>

sigaction is called without SA_RESTART, but the syscall is restarted anyway...
Apart from removing those tests, I don't see what we can do here.