preflight memory check: units problems

/proc/meminfo reports kibibytes. Lower the minimum memory requirement so that 768 MB (not MiB) also is allowed.

Report the detected memory in MB (not KiB), to be clearer.

Fixes #289.

setup/preflight.sh

@@ -17,13 +17,19 @@ if [ "`lsb_release -d | sed 's/.*:\s*//' | sed 's/14\.04\.[0-9]/14.04/' `" != "U
 	exit
 fi
 
-# Check that we have enough memory. Skip the check if we appear to be
-# running inside of Vagrant, because that's really just for testing.
+# Check that we have enough memory.
+#
+# /proc/meminfo reports free memory in kibibytes. Our baseline will be 768 KB,
+# which is 750000 kibibytes.
+#
+# Skip the check if we appear to be running inside of Vagrant, because that's really just for testing.
 TOTAL_PHYSICAL_MEM=$(head -n 1 /proc/meminfo | awk '{print $2}')
-if [ $TOTAL_PHYSICAL_MEM -lt 786432 ]; then
+if [ $TOTAL_PHYSICAL_MEM -lt 750000 ]; then
 if [ ! -d /vagrant ]; then
-	echo "Your Mail-in-a-Box needs more than $TOTAL_PHYSICAL_MEM MB RAM."
+	TOTAL_PHYSICAL_MEM=$(expr \( \( $TOTAL_PHYSICAL_MEM \* 1024 \) / 1000 \) / 1000)
+	echo "Your Mail-in-a-Box needs more memory (RAM) to function properly."
 	echo "Please provision a machine with at least 768 MB, 1 GB recommended."
+	echo "This machine has $TOTAL_PHYSICAL_MEM MB memory."
 	exit
 fi
 fi