Make the self-updating function a bit more robust

youtube-dl

@@ -2296,20 +2296,26 @@ if __name__ == '__main__':
 		import getpass
 		import optparse
 
-		# Function to update the program file with the latest version from bitbucket.org
+		# Function to update the program file with the latest version from the repository.
 		def update_self(downloader, filename):
 			# Note: downloader only used for options
 			if not os.access(filename, os.W_OK):
 				sys.exit('ERROR: no write permissions on %s' % filename)
 
 			downloader.to_screen('Updating to latest stable version...')
+			try:
 				latest_url = 'http://github.com/rg3/youtube-dl/raw/master/LATEST_VERSION'
 				latest_version = urllib.urlopen(latest_url).read().strip()
 				prog_url = 'http://github.com/rg3/youtube-dl/raw/%s/youtube-dl' % latest_version
 				newcontent = urllib.urlopen(prog_url).read()
+			except (IOError, OSError), err:
+				sys.exit('ERROR: unable to download latest version')
+			try:
 				stream = open(filename, 'w')
 				stream.write(newcontent)
 				stream.close()
+			except (IOError, OSError), err:
+				sys.exit('ERROR: unable to overwrite current version')
 			downloader.to_screen('Updated to version %s' % latest_version)
 
 		# Parse command line