[bgen] Make --reference work as well as -r. (#8045)

It took me a while to figure out why my newly added references didn't quite
work as expected... so let's make sure future me doesn't run into the same
problem again.

src/btouch.cs

@@ -242,7 +242,7 @@ public class BindingTouch {
 			{ "ns=", "Sets the namespace for storing helper classes", v => ns = v },
 			{ "unsafe", "Sets the unsafe flag for the build", v=> unsafef = true },
 			{ "core", "Use this to build product assemblies", v => BindThirdPartyLibrary = false },
-			{ "r=", "Adds a reference", v => references.Add (v) },
+			{ "r|reference=", "Adds a reference", v => references.Add (v) },
 			{ "lib=", "Adds the directory to the search path for the compiler", v => libs.Add (v) },
 			{ "compiler=", "Sets the compiler to use (Obsolete) ", v => compiler = v, true },
 			{ "sdk=", "Sets the .NET SDK to use (Obsolete)", v => {}, true },