Reject MOVE to non-integer DBs

Previously, "MOVE key somestring" would move the key to
DB 0 which is just unexpected and wrong.
String as DB == error.

Test added too.

Modified by @antirez in order to use the getLongLongFromObject() API
instead of strtol().

Fixes #1428

tests/unit/basic.tcl

@@ -404,6 +404,12 @@ start_server {tags {"basic"}} {
         r move mykey 10
     } {0}
 
+    test {MOVE against non-integer DB (#1428)} {
+        r set mykey hello
+        catch {r move mykey notanumber} e
+        set e
+    } {*ERR*index out of range}
+
     test {SET/GET keys in different DBs} {
         r set a hello
         r set b world