During initial check of key, don't dump it to stdout.

Change-Id: I82e37c0eb789e5bd47869a7b9c4d54235c3ca07a
Support both whole-line and line-trailing comments.

Whole-line comments are obviosuly useful, and trailing lines useful to
annotate specific recipient (e.g., with readable identifier, if recipient is
given via key ID).

Change-Id: I09901daaa910f39889470956d9d9c94e14df77e3