Re-use previous configuration as defaults

configure

@@ -15,13 +15,24 @@ COMMENT=""
 
 echo -n > $TEMPFILE
 
+get_default() {
+    V=$1
+    if ! [[ -e config.mk ]]; then
+        return ""
+    fi
+    grep "$V = " config.mk | sed -e 's/.* = \+//'
+}
+
 while read LINE <&4; do
     if echo "$LINE" | grep -q '^#'; then
         COMMENT=$(echo "$LINE" | sed -e 's/^#\+ *//')
     elif echo "$LINE" | grep -q '^[0-9A-Z_]\+ *= *'; then
 
         VARNAME=$(echo "$LINE" | sed -e 's/ *=.*//')
+        DEFAULT="$(get_default $VARNAME)"
+        if [[ -z "$DEFAULT" ]]; then
             DEFAULT=$(echo "$LINE" | sed -e 's/^[0-9A-Z_]\+ *= *//')
+        fi
 
         # if there are prefix vars that are false, we need to skip
         SKIP=0