libxfs-apply: auto-name patches for guilt

libxfs-apply: auto-name patches for guilt

When applying a series of commits, having to write a name for each
of them is time consuming. instead, just use the same method
'guilt import-commit' uses and use the commit header to generate the
filename automatically.

Again, this is simply lifted from guilt....

Signed-off-by: Dave Chinner <david@fromorbit.com>