Refactoring box pattern match to compile with Rust 1.19 stable version

[sanketr]

Since Rust is pretty stable now, I tried compiling this library with latest version of the compiler. However, there are some experimental features such as box pattern match that need to be refactored to make it compile with stable version. Since my knowledge of Rust borrow checker is still not very good, I am unable to figure out how to refactor the box pattern match for kdict in kbindings.

Help will be very much appreciated with refactoring the code to make it work with stable version.