mke2fs: Fix up the fs type and feature selection for 64-bit blocks

We need to defer setting the blocks count field in the fs_param
structure until it is known whether 64-bit feature will be enabled
(and whether the blocks count is valid).

We also add a new mke2fs.conf configuration parameter,
auto_64-bit_support which will automatically enable the 64-bit feature
if the number of blocks requires it.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/misc/mke2fs.conf.5.in b/misc/mke2fs.conf.5.in
index c1b54f7..d212947 100644
--- a/misc/mke2fs.conf.5.in
+++ b/misc/mke2fs.conf.5.in
@@ -303,6 +303,14 @@
 command-line option to
 .BR mke2fs (8).
 .TP
+.I auto_64-bit_support
+This relation is a boolean which specifies whether
+.BR mke2fs (8)
+should automatically add the 64bit feature if the number of blocks for
+the file system requires this feature to be enabled.  The resize_inode
+feature is also automatically disabled since it doesn't support 64-bit
+block numbers.
+.TP
 .I blocksize
 This relation specifies the default blocksize if the user does not
 specify a blocksize on the command line.