Add blowfish as a usable encryption cipher.

Add blowfish to the available encryption ciphers, with all of its
supported modes, like ecb, cbc, ofb and cfb64.
Update the usage help and the manual accordingly. Also reword some
stuff, now that there is more than one encryption cipher available.

(cherry picked from commit 5eca59f928542659866ccb758d6e3bf9b7cf93a0)
'passwd' can not be used to change the cipher and/or its mode anymore.

(cherry picked from commit baac326ef535af38803a6e9eecb86618495f09c2)
Fix the 'export' cmd usage to reflect the reality.

(cherry picked from commit d24069e8a8cc7bff4c67eeb146ebc753b048845f)
Shorten the usage help. The manual has the details.

(cherry picked from commit 96ab0504140670430bea8303b79fd894e4e6277a)
Add a comma to the manual.

(cherry picked from commit 9115cc68af05982621877169c2ee5c846e863ac0)
Fix the 'export' command's usage the command help too.

(cherry picked from commit 40ecce2e98b9c04c6fd8ad01185a2cd1a2ec0449)
Extend Changelog with blowfish enc. cipher.