Fix #25: be more defensive
Fix #26: suppress same file warnings
Remove ggtags-enable-completion-at-point
Fix #25: check display-buffer-no-window availability
Compatible with emacs 24.1 and 24.2
Ensure global buffer is shown in case of error

Use relative path in ggtags-browse-file-as-hypertext.
Doc fix.
Force ggtags-update-tags when called interactively