[PATCH] On linux require the libc to have large file support

With this, support code in grub-core/osdep/unix/hostdisk.c for old glibc releases could be removed. --- This patch tries to address the issues raised in http://lists.gnu.org/archive/html/grub-devel/2014-12/msg00030.html --- INSTALL | 1 + configure.ac|

enable cryptomount to read passphrase from file

Here's a compile-tested patch that attempts to add '-p FILE' support to cryptomount, so that the passphrase can be read from a usb key or somesuch. I was unsure about how much to massage or verify the file, say, dropping a trailing newline or truncating the passphrase at the first newline or whate