Work around sqlite's incorrect handling of umask when creating databases.

Refactored some common code into initDb.

This only deals with the problem when creating new databases. If a repo
got bad permissions into it, it's up to the user to deal with it.

This commit was sponsored by Ole-Morten Duesund on Patreon.

Utility/FileMode.hs

@@ -1,6 +1,6 @@
 {- File mode utilities.
  -
- - Copyright 2010-2012 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2017 Joey Hess <id@joeyh.name>
  -
  - License: BSD-2-clause
  -}
@@ -130,6 +130,21 @@ withUmask umask a = bracket setup cleanup go
 withUmask _ a = a
 #endif
 
+getUmask :: IO FileMode
+#ifndef mingw32_HOST_OS
+getUmask = bracket setup cleanup return
+  where
+	setup = setFileCreationMask nullFileMode
+	cleanup = setFileCreationMask
+#else
+getUmask = return nullFileMode
+#endif
+
+defaultFileMode :: IO FileMode
+defaultFileMode = do
+	umask <- getUmask
+	return $ intersectFileModes (complement umask) stdFileMode
+
 combineModes :: [FileMode] -> FileMode
 combineModes [] = 0
 combineModes [m] = m