[submit_gmx_analyses_lintf2_ether.py]: Change Default of --every

Change the default value of the `--every` option from 0 to 1.

The value of the `--every` option is passed to the `-dt` option of the
submitted Gromacs tools that support this option.  The default value was
set to 0 in PR #74
(#74),
because `gmx trjconv` did not process all frames when `-dt` was set to 1
and the spacing between trajectory frames was less than 1 ps.

However, it now turned out that the other Gromacs tools only process the
first frame when `-dt` is set to 0.  Therefore, we reset the default
value for `--every` (i.e. `-dt`) to 1.

In a following commit, we will replace the `-dt` option for `gmx
trjconv` with `-skip`, which should be more robust (see
https://www.mail-archive.com/gmx-users@gromacs.org/msg35903.html and
https://www.mail-archive.com/gmx-users@gromacs.org/msg06868.html).

Author: andthum

analysis/lintf2_ether/gmx/submit_gmx_analyses_lintf2_ether.py

@@ -57,8 +57,12 @@
     :file:`${settings}_out_${system}.log`.  Reading from |log_file|\s
     compressed with gzip, bzip2, XZ or LZMA is supported.
 --every
-    Only use frame if t MOD every == first time (in ps).  Default:
-    ``0``.
+    Read every n-th frame from the trajectory.  The value given here is
+    passed to the -skip option of the submitted Gromacs tools that
+    support this option.  If the -skip option is not supported, the
+    value of \--every is passed to the -dt option.  For Gromacs tools
+    that do not support either of the two options, \--every has no
+    effect.  Default: ``1``.
 
 Options for MSD Calculation
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -455,12 +459,11 @@ def _submit(sbatch_opts, job_script):
     )
     parser_trj_reading.add_argument(
         "--every",
-        type=float,
+        type=int,
         required=False,
-        default=0,
+        default=1,
         help=(
-            "Only use frame if t MOD every == first time (in ps).  Default:"
-            " %(default)s."
+            "Read every n-th frame from the trajectory.  Default: %(default)s."
         ),
     )
     parser_msd = parser.add_argument_group(title="Options for MSD Calculation")