Fixes done for security issues review comments. 
Comments provided by Dustin. J. Mitchell-
1. It would probably be better to use the preprocessor conditionals (`#if defined(DUMP)`, etc.) here instead of trying to figure out which program is in use at runtime. If an Amanda install is set up with, say, XFSDUMP=/opt/fs/old-xfsdump, then the code above would never call `validate_xfsdump_options`, even though it's clear that it's driving xfsdump.
2. Why not have the `validate_..` functions call `error(..)` themselves, rather than printing something (which might get lost) and then giving a blank error message (or more oddly, a single space character??) here? Alternately, `validate_..` could return an allocated error message.

Fixed issue:
1. Using getopt() to check the command option failed to check the blacklist option if the command is provided like:
/usr/lib/amanda/rundump NOCONFIG xfsdump -0f /dev/null /sys -F "echo test"
It was working fine when the command is provided like:
/usr/lib/amanda/rundump NOCONFIG xfsdump -0f /dev/null -F "echo test" /sys

git-svn-id: svn+ssh://svn.code.sf.net/p/amanda/code/amanda/branches/3_5@7716 a8d146d6-cc15-0410-8900-af154a0219e0