OpenPGP: re-factor pgp_select_file()
OpenPGP: re-factor pgp_select_file()

* remove unnecessary copy operations with a temporary path object,
  instead increase the start index.
* addd comments

Signed-off-by: Peter Marschall <peter@adpm.de>

git-svn-id: 444ed946b9c2220da791e84c3dd156a05f92db99@5489 c6295689-39f2-0310-b995-f0e70906c6a9

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