Improve efficiency of checking for access to authority documents

Improve efficiency of checking for access to authority documents

* java/org/gnu/emacs/EmacsService.java (checkContentUri): Take a
string instead of a byte array.  Then, use
checkCallingUriPermission, in lieu of opening the file.
* src/android.c (android_check_content_access): Delete unused
function.
(android_init_emacs_service): Adjust for changes to
checkContentUri's signature.
* src/androidvfs.c (android_get_content_name): Return the file
name in a new buffer.
(android_check_content_access): Adjust correspondingly.
(android_authority_name): Verify NAME is a valid JNI string.