fixed Gromacs 5.x syntax for MDrunner

Although MDrunner is not configurable, it should work most of the
time with default setup (i.e., with the 'gmx' driver command).

For anything else, derive a new class.

Closes #65 (can be reopened if demand is there)

gromacs/run.py

@@ -94,12 +94,10 @@ class MDrunner(utilities.FileUtils):
     :attr:`mdrun`. This can be a single string or a sequence (tuple) of
     strings. On instantiation, the first entry in :attr:`mdrun` that can be
     found on the :envvar:`PATH` is chosen (with
-    :func:`find_gromacs_command`). The entries can follow the config file
-    syntax and denote a *driver* command (for Gromacs 5.x) that is separated
-    from the command name itself by a colon. For example, ``gmx:mdrun`` from
+    :func:`find_gromacs_command`). For example, ``gmx mdrun`` from
     Gromacs 5.x but just ``mdrun`` for Gromacs 4.6.x. Similarly, alternative
     executables (such as double precision) need to be specified here
-    (e.g. ``("mdrun_d", "gmx_d:mdrun")``).
+    (e.g. ``("mdrun_d", "gmx_d mdrun")``).
 
     .. Note:: Changing :program:`mdrun` arguments permanently changes the
               default arguments for this instance of :class:`MDrunner`. (This
@@ -109,14 +107,16 @@ class MDrunner(utilities.FileUtils):
        Added detection of bare Gromacs commands (Gromacs 4.6.x) or commands run through
        :program:`gmx` (Gromacs 5.x).
 
+    .. versionchanged:: 0.6.0
+       Changed syntax for Gromacs 5.x commands.
     """
 
     #: Path to the :program:`mdrun` executable (or the name if it can be found on :envvar:`PATH`);
-    #: this can be a tuple and then the program names are tried in sequence. You can use
-    #: the syntax from the config file ``gmx:mdrun`` to designate a driver command.
+    #: this can be a tuple and then the program names are tried in sequence. For Gromacs 5
+    #: prefix with the driver command, e.g., ``gmx mdrun``.
     #:
     #: .. versionadded:: 0.5.1
-    mdrun = ("mdrun", "gmx:mdrun")
+    mdrun = ("mdrun", "gmx mdrun")
     #: path to the MPI launcher (e.g. :program:`mpiexec`)
     mpiexec = None
 
@@ -278,14 +278,14 @@ def check_success(self):
 
 class MDrunnerDoublePrecision(MDrunner):
     """Manage running :program:`mdrun_d`."""
-    mdrun = ("mdrun_d", "gmx_d:mdrun")
+    mdrun = ("mdrun_d", "gmx_d mdrun")
 
 class MDrunnerOpenMP(MDrunner):
     """Manage running :program:`mdrun` as an OpenMP_ multiprocessor job.
 
     .. _OpenMP: http://openmp.org/wp/
     """
-    mdrun = ("mdrun_openmp", "gmx_openmp:mdrun")
+    mdrun = ("mdrun_openmp", "gmx_openmp mdrun")
     mpiexec = "mpiexec"
 
 class MDrunnerMpich2Smpd(MDrunner):