bash: export environment variables in a way that bash understands

* also set xterm as TERM

Change-Id: I39f06a5eab7a1e0920593bf0a52df7e9d780da99

etc/bashrc

@@ -5,12 +5,11 @@
 # that can't tolerate any output.  So make sure this doesn't display
 # anything or bad things will happen !
 
-: ${HOME:=/sdcard}
-: ${HOSTNAME:=$(getprop ro.cm.device)}
-: ${TERM:=linux}
-: ${TMPDIR:=/data/local/tmp}
-: ${USER:=$(id -un)}
-export HOME HOSTNAME MKSH SHELL TERM TMPDIR USER
+export HOME=/sdcard
+export HOSTNAME=$(getprop ro.cm.device)
+export TERM=xterm
+export TMPDIR=/data/local/tmp
+export USER=$(id -un)
 
 # Test for an interactive shell.  There is no need to set anything
 # past this point for scp and rcp, and it's important to refrain from