Fixes the following test failure occurring on Ubuntu 10.10 64-bit:
Fixes the following test failure occurring on Ubuntu 10.10 64-bit:

======================================================================
FAIL: test_exe (__main__.TestCase)

Traceback (most recent call last):
  File "test/test_psutil.py", line 370, in test_exe
      % (repr(p.exe), p.pid, p.name, p.cmdline))
      % AssertionError: '/usr/bin/pulseaudio (deleted)' does not exist (pid=1481, name=pulseaudio, cmdline=['/usr/bin/pulseaudio', '--start', '--log-target=syslog'])


Added a check when reading /proc/PID/exe symlink which makes sure the executable exists in case '(deleted)' appears in the path string.

ztop/psutil,ztop/psutil,ztop/psutil,ztop/psutil