ENH - utilize persistent variables for speedup (fieldtrip#2192)

* ENH - utilize persistent variables for speedup

* ENH - initialize persistent variable to false, just to be sure

ft_defaults.m

@@ -82,13 +82,13 @@
 end
 
 % ft_warning is located in fieldtrip/utilities, which may not be on the path yet
-if ~exist('ft_warning', 'file')
+if ~initialized && ~exist('ft_warning', 'file')
   ft_warning = @warning;
 end
 
 % locate the file with the persistent FieldTrip preferences
 fieldtripprefs = fullfile(prefdir, 'fieldtripprefs.mat');
-if exist(fieldtripprefs, 'file')
+if ~initialized && exist(fieldtripprefs, 'file')
   prefs       = load(fieldtripprefs); % the file contains multiple fields
   ft_default  = mergestruct(ft_default, prefs);
 end

utilities/memtic.m

@@ -59,14 +59,23 @@
 % $Id$
 
 persistent state
+persistent mexfile_exists
 
 if nargin<1
   action = 'tic';
 end
 
+if isempty(mexfile_exists)
+  mexfile_exists = false;
+end
+
+if ~mexfile_exists
+  mexfile_exists = isempty(strfind(which('memprofile'), mexext));
+end
+
 % the memtic/memtoc functions make use of a low-level mex file that interacts directly with the operating system
 % do not fail if the mex file does not exist
-if isempty(strfind(which('memprofile'), mexext))
+if mexfile_exists
   switch action
     case 'tic'
       if nargout