Bug 675691 - Get rid of mozconfig guesswork. r=ted

- MOZCONFIG is now the only environment variable we recognize. We used to
  recognize MOZ_MYCONFIG as well, but we now error out if that is set.

- $topsrcdir/.mozconfig is now the only implicit location we recognize. We used
  to recognize a number of other implicit locations, but we now error out where
  we would have used one of them.

build/autoconf/mozconfig-find

@@ -42,7 +42,6 @@
 #    order:
 #       if $MOZCONFIG is set, use that.
 #       Otherwise, use $TOPSRCDIR/.mozconfig
-#       Otherwise, use $HOME/.mozconfig
 #
 topsrcdir=$1
 
@@ -67,19 +66,29 @@ abspath() {
   echo `pwd`/$1
 }
 
+if [ -n "$MOZCONFIG" ] && ! [ -f "$MOZCONFIG" ]; then
+  echo "Specified MOZCONFIG \"$MOZCONFIG\" does not exist!"
+  exit 1
+fi
+
+if [ -n "$MOZ_MYCONFIG" ]; then
+  echo "Your environment currently has the MOZ_MYCONFIG variable set to \"$MOZ_MYCONFIG\". MOZ_MYCONFIG is no longer supported. Please use MOZCONFIG instead."
+  exit 1
+fi
+
 for _config in "$MOZCONFIG" \
-               "$MOZ_MYCONFIG"
+               "$topsrcdir/.mozconfig"
 do
-  if [ -n "$_config" ] && ! [ -f "$_config" ]; then
-    echo "Specified MOZCONFIG \"$_config\" does not exist!"
-    exit 1
+  if test -f "$_config"; then
+    echo `abspath $_config`
+    exit 0
   fi
 done
 
-for _config in "$MOZCONFIG" \
-               "$MOZ_MYCONFIG" \
-               "$topsrcdir/.mozconfig" \
-               "$topsrcdir/mozconfig" \
+# We used to support a number of other implicit .mozconfig locations. We now
+# detect if we were about to use any of these locations and issue an error if we
+# find any.
+for _config in "$topsrcdir/mozconfig" \
                "$topsrcdir/mozconfig.sh" \
                "$topsrcdir/myconfig.sh" \
                "$HOME/.mozconfig" \
@@ -87,7 +96,7 @@ for _config in "$MOZCONFIG" \
                "$HOME/.mozmyconfig.sh"
 do
   if test -f "$_config"; then
-    echo `abspath $_config`
-    exit 0
+    echo "You currently have a mozconfig at \"$_config\". This implicit location is no longer supported. Please move it to $topsrcdir/.mozconfig or specify it explicitly via \$MOZCONFIG.";
+    exit 1
   fi
 done