vcs-svn: allow input errors to be detected promptly

The line_buffer library silently flags input errors until
buffer_deinit time; unfortunately, by that point usually errno is
invalid.  Expose the error flag so callers can check for and
report errors early for easy debugging.

	some_error_prone_operation(...);
	if (buffer_ferror(buf))
		return error("input error: %s", strerror(errno));

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

vcs-svn/line_buffer.c

@@ -59,6 +59,11 @@ long buffer_tmpfile_prepare_to_read(struct line_buffer *buf)
 	return pos;
 }
 
+int buffer_ferror(struct line_buffer *buf)
+{
+	return ferror(buf->infile);
+}
+
 int buffer_read_char(struct line_buffer *buf)
 {
 	return fgetc(buf->infile);