Add support for shortened page sizes for commandline uilities (at least GBAK)

[TommiPrami]

Hello,

Used to know powers of twos up to guite big numbers by heart. Don't remember anymore, so would help if there would be same shorthand as in the conf-files.

Like:

-PAGE_SIZE 16K

etc... Would be so easy to remember, once supported. Not that big thing but when got used to using those in the .conf files, I really do not want to remember those exact numbers anymore (or do google searches every time needed).

If already supported, should be documented.

-Tee-