internal/mobileinit,bind/java,app: don't treat jobject as a pointer

On Android, the JNI jobject type doesn't always contain a pointer.
Treating a non-pointer as a pointer can crash the runtime. Use
the more appropriate type uintptr instead.

Change-Id: I2b2049918d60226c4d23d6df0b10e68248d54bc2
Reviewed-on: https://go-review.googlesource.com/110256
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

bind/java/context_android.go

@@ -17,5 +17,5 @@ import (
 
 //export setContext
 func setContext(vm *C.JavaVM, ctx C.jobject) {
-	mobileinit.SetCurrentContext(unsafe.Pointer(vm), unsafe.Pointer(ctx))
+	mobileinit.SetCurrentContext(unsafe.Pointer(vm), uintptr(ctx))
 }