enh: Add support for spm/mcr config via env vars

This patch adds support for configuring the SPM standalone version (mcr)
via environment variables. The respected environment variables are:

    USE_SPMMCR: any value, sets use_mcr to True
    SPMMCRCMD:  command to use for spm mcr, if use_mcr is True

Author: rku

nipype/interfaces/spm/base.py

@@ -129,22 +129,34 @@ def version(matlab_cmd=None, paths=None, use_mcr=None):
 
         Parameters
         ----------
-        matlab_cmd : String specifying default matlab command
-
-            default None, will look for environment variable MATLABCMD
-            and use if found, otherwise falls back on MatlabCommand
-            default of 'matlab -nodesktop -nosplash'
+        matlab_cmd: str
+            Sets the default matlab command. If None, the value of the
+            environment variable SPMMCRCMD will be used if set and use_mcr
+            is True or the environment variable USE_SPMMCR is set.
+            If one of USE_SPMMCR or SPMMCRCMD is not set, the existence
+            of the environment variable MATLABCMD is checked and its value
+            is used as the matlab command if possible.
+            If none of the above was successful, the fallback value of
+            'matlab -nodesktop -nosplash' will be used.
+        paths : str
+        use_mcr : bool
 
         Returns
         -------
         spm_path : string representing path to SPM directory
 
             returns None of path not found
         """
+        if use_mcr or 'USE_SPMMCR' in os.environ:
+            use_mcr = True
+            try:
+                matlab_cmd = os.environ['SPMMCRCMD']
+            except KeyError:
+                pass
         if matlab_cmd is None:
             try:
                 matlab_cmd = os.environ['MATLABCMD']
-            except:
+            except KeyError:
                 matlab_cmd = 'matlab -nodesktop -nosplash'
         mlab = MatlabCommand(matlab_cmd=matlab_cmd)
         mlab.inputs.mfile = False