scmutil: narrow ImportError handling in termwidth()

The array module must exist. It's sufficient to suppress the ImportError of
termios. Also salvaged the comment why we have to handle AttributeError, from
7002bb17cc5e.

mercurial/scmposix.py

@@ -1,72 +1,72 b''
 from __future__ import absolute_import
 
+import array
 import errno
 import fcntl
 import os
 import sys
 
 from . import (
     encoding,
     osutil,
 )
 
 def _rcfiles(path):
     rcs = [os.path.join(path, 'hgrc')]
     rcdir = os.path.join(path, 'hgrc.d')
     try:
         rcs.extend([os.path.join(rcdir, f)
                     for f, kind in osutil.listdir(rcdir)
                     if f.endswith(".rc")])
     except OSError:
         pass
     return rcs
 
 def systemrcpath():
     path = []
     if sys.platform == 'plan9':
         root = 'lib/mercurial'
     else:
         root = 'etc/mercurial'
     # old mod_python does not set sys.argv
     if len(getattr(sys, 'argv', [])) > 0:
         p = os.path.dirname(os.path.dirname(sys.argv[0]))
         if p != '/':
             path.extend(_rcfiles(os.path.join(p, root)))
     path.extend(_rcfiles('/' + root))
     return path
 
 def userrcpath():
     if sys.platform == 'plan9':
         return [encoding.environ['home'] + '/lib/hgrc']
     else:
         return [os.path.expanduser('~/.hgrc')]
 
 def termwidth(ui):
     try:
-        import array
         import termios
+        TIOCGWINSZ = termios.TIOCGWINSZ  # unavailable on IRIX (issue3449)
+    except (AttributeError, ImportError):
+        return 80
+    if True:
         for dev in (ui.ferr, ui.fout, ui.fin):
             try:
                 try:
                     fd = dev.fileno()
                 except AttributeError:
                     continue
                 if not os.isatty(fd):
                     continue
-                try:
-                    arri = fcntl.ioctl(fd, termios.TIOCGWINSZ, '\0' * 8)
+                if True:
+                    arri = fcntl.ioctl(fd, TIOCGWINSZ, '\0' * 8)
                     width = array.array('h', arri)[1]
                     if width > 0:
                         return width
-                except AttributeError:
-                    pass
             except ValueError:
                 pass
             except IOError as e:
                 if e[0] == errno.EINVAL:
                     pass
                 else:
                     raise
-    except ImportError:
-        pass
     return 80