Fixes for in-memory databases

In-memory databases always allow write access and don't need to
use lock files.

gramps/gen/db/generic.py

@@ -587,6 +587,9 @@ class DbGeneric(DbWriteBase, DbReadBase, UpdateCallback, Callback):
         Return True if we don't have read/write access to the database,
         otherwise return False (that is, we DO have read/write access)
         """
+        # In-memory databases always allow write access.
+        if name == ':memory:':
+            return False
 
         # See if we write to the target directory at all?
         if not os.access(name, os.W_OK):
@@ -616,7 +619,7 @@ class DbGeneric(DbWriteBase, DbReadBase, UpdateCallback, Callback):
 
         self.readonly = mode == DBMODE_R
 
-        if not self.readonly:
+        if not self.readonly and directory != ':memory:':
             write_lock_file(directory)
 
         # run backend-specific code: