import-checker: force 'fcntl', 'grp', 'pwd', and 'termios' to stdlib modules

These are Unix only, and caused these additional warnings on Windows if they
aren't hardcoded as stdlib:

  mercurial/posix.py mixed imports
     stdlib:    errno, getpass, os, socket, stat, sys, tempfile
     relative:  grp, pwd, unicodedata
  mercurial/posix.py mixed imports
     stdlib:    re
     relative:  fcntl
  mercurial/posix.py mixed imports
     stdlib:    array
     relative:  termios

Additionally, this was missing on Windows:

  mercurial/crecord.py mixed imports
     stdlib:    fcntl, termios
     relative:  curses


https://docs.python.org/2/library/fcntl.html
https://docs.python.org/2/library/grp.html
https://docs.python.org/2/library/pwd.html
https://docs.python.org/2/library/termios.html

contrib/import-checker.py

@@ -61,6 +61,8 b' def list_stdlib_modules():'
     for m in 'ctypes', 'email':
         yield m
     yield 'builtins' # python3 only
+    for m in 'fcntl', 'grp', 'pwd', 'termios':  # Unix only
+        yield m
     stdlib_prefixes = set([sys.prefix, sys.exec_prefix])
     # We need to supplement the list of prefixes for the search to work
     # when run from within a virtualenv.