security/gnupg: Create symlink for manpage

When security/gnupg1 isn't installed, ${PREFIX}/bin/gpg symlink is
created whose target is 'gpg2'. It means gpg2 can also be invoked as
'gpg'. And under such situation it is convenient for user if gpg2(1)
man page can also be accessed as gpg(1). So create
${PREFIX}/man/man1/gpg.1.gz symlink whose target is 'gpg2.1.gz'.

PR:		272519
Approved by:	maintainer timeout