Fix check for dmenu (open file mode, dependency on which).

See <https://github.com/proxypoke/quickswitch-for-i3/pull/24>.

--- quickswitch-i3-2.2/quickswitch.py	2016-09-18 19:59:10.257765542 +0200
+++ quickswitch-i3-2.2/quickswitch.py	2016-09-21 10:43:01.277577819 +0200
@@ -24,9 +24,10 @@
 
 import argparse
 import subprocess
-import os
 import re
 
+from distutils.spawn import find_executable
+
 try:
     import i3
 except ImportError:
@@ -37,11 +38,8 @@
 
 def check_dmenu():
     '''Check if dmenu is available.'''
-    devnull = open(os.devnull)
-    retcode = subprocess.call(["which", "dmenu"],
-                              stdout=devnull,
-                              stderr=devnull)
-    return True if retcode == 0 else False
+    executable = find_executable("dmenu")
+    return executable != None
 
 
 def dmenu(options, dmenu):
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<tr><td><span title='2023-01-30 22:24:27 +0100'>2023-01-30</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=0ef8fe22ed8985c9656835fc25ab3463d55b6669'>linux-container: 'container-excursion' forks to join the PID namespace.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-01-30 22:24:27 +0100'>2023-01-30</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=52eb3db19cb9e5c294c86a8552a4baaa5b473672'>container: Correctly report exit status.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-09-24 17:59:04 +0200'>2022-09-24</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=00d5bb5d7f18555c250b4a6ef0b33b628acc3a3a'>linux-container: Mark socket pair as SOCK_CLOEXEC.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-09-20 19:24:31 +0200'>2022-09-20</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=6abdcef4a68e98f538ab69fde096adc5f5ca4ff4'>linux-container: 'container-excursion*' marks its FDs as FD_CLOEXEC.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-05-01 21:30:35 +0200'>2022-05-01</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=391bd143592241a5bf3555918a5188c789c1c771'>linux-container: Add #:child-is-pid1? parameter to 'call-with-container'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-05-01 21:30:35 +0200'>2022-05-01</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=f6c9763984dafe5023e171878231cbcc6cc1edfa'>linux-container: Ensure signal-handling asyncs get a chance to run.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-05-01 21:30:34 +0200'>2022-05-01</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=a76fa226c8761dd349aaacca7ba041429bce4e73'>linux-container: 'call-with-container' relays SIGTERM and SIGINT.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-01-05 23:44:18 +0100'>2022-01-05</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=bfdeba11f86b18172194b416c6eb59b7cc7ef355'>linux-container: Handle CLONE_NEWCGROUP and use it by default.</a><span class='msg-avail'>...</span></td><td>Ryan Sundberg</td></tr>
<tr><td><span title='2020-12-06 21:55:18 +0100'>2020-12-06</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=329fa5bdbb621dae586cbfb062cbd3b295880ba5'>Revert "linux-container: Correct test for unprivileged user namespace support."</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-12-03 16:25:45 +0000'>2020-12-03</span></td><td><a href='/guix/commit/gnu/build/linux-container.scm?id=8bc5ca5160db3d82bd5b6b2b7ed80c96f42bd33e'>linux-container: Correct test for unprivileged user namespace support.</a><span class='msg-avail'>...</span></td><td>Paul Garlick</td></tr>