Suppress error if preference checkforrecoveries is undefined.

It appears this preference is not always defined, like on certain
Linux distributions or installation on Windows using a classkit
license. See issue #39. We just suppress the error as the whole
point is to not have recovery files anyway, seeing as how they might
use up all disk space when many simulations are run back to back.

mph/client.py

@@ -137,7 +137,11 @@ def __init__(self, cores=None, version=None, port=None, host='localhost'):
         java.setPreference('updates.update.check', 'off')
         java.setPreference('tempfiles.saving.warnifoverwriteolder', 'off')
         java.setPreference('tempfiles.recovery.autosave', 'off')
-        java.setPreference('tempfiles.recovery.checkforrecoveries', 'off')
+        try:
+            # Preference not defined on certain systems, see issue #39.
+            java.setPreference('tempfiles.recovery.checkforrecoveries', 'off')
+        except Exception:
+            logger.debug('Could not turn off check for recovery files.')
         java.setPreference('tempfiles.saving.optimize', 'filesize')
 
         # Save useful information in instance attributes.