gpg: Re-indent check_key_signature2.

I am considering some changes and thus better start off by switching
to standard GNU indentation. This patch also changes comment lines
like

if (foo)
  /* Comment on foo.  */
  {

to

if (foo)
  { /* Comment on foo.  */

or

if (foo) /* Comment on foo.  */
  {

to make the brace of the opening block stand out immediately.

Further stars on the left are added to longer comments because that
makes the code easier to read by disabled hackers, when reading
without font locking, and for reading black-white printouts.